PROPOSAL FOR THE RESTORA TION OF MARCUS · PDF fileSTRUCTURAL ANALYSIS OF HISTORICAL CONSTRUCTIONS P. Roca, J.L. González, A.R. Marí and E. Onale (Eds.) Q C1MNE, Barcelona 1996...

STRUCTURAL ANALYSIS OF HISTORICAL CONSTRUCTIONS P. Roca, J.L. González, A.R. Marí and E. Onale (Eds.)

Q C1MNE, Barcelona 1996

PROPOSAL FOR THE RESTORA TION OF MARCUS AURELIUS'S COLUMN

A. Guiffre Universita Terza di Roma

Italy

S U MMÁRY

Two monumental columns have been built in Rome sincc the second century AD: Trajan's Column and t he Marcus Aurelius's Column. Their construction technique is examined fi rst, and thell the state of damage. The two columns, standing less then 700 m apart, have withstood a li t he earthquakes that have shaken Rome since they were built, but the type of damagc t hat they have suffered is different . Marcus Aurelius's Column has suffered a great deal more cracki ng thall the other. A debate is going on at present among the cxperts regarding the reasons for this different behaviour, and in this pa per a position is taken on the subject. The results of studies and experiments rcgarding the seismic response of the columns are also discussed . The restoration by Fontana in 1590 is illust rated anel the present state Df safety of the columns is discussed. From all the analyses and t he hypotheses previously presenteei, a p roposal for a new restoration aimed at seismic safety is inferred. The condusion presents the author' s opinion on t he proper way to study such a monument with a view to restoring it.

1.- THE C ONSTRUCTION TEC HNIQUE

There is no doubt that because of tht: naLurc of iL~ consLruction and its

commemorative conception Marcus Au rclius's Column must be a t tributed to Apollodorus of Damascus, li ke the prototype dedicated to Trajan in 113 AD.

In both colu mns, sevcnteen marble stones, each weighing 40 metric tons, were transportcd from the Lunigiana (from the caves of the modern Carrara) to the centre of Rome. They were first t aken by boat along the Et ruscan coast and

up the Tiber I anel thcn dragged from the Tes taccio to the piazza Colonoa.

This operation also involved the blocks of the pedestal, even largcr and heavier ,

anel the square abacus, and the rounded top on which the bronze statue of

A. GUIFFRE I Mareus Aurclius's Column 271

M areus was plaeed.

It was earved in a eylindrieal form on ,· ... hieh the battles and the "miracles"

of the emperor would be seulpted, and was hollowed out until the weight was redueed to about 27t to house the spiraI stairease that reeaUs an Arehimedes

serew The massive stones \Vere lifted with the polypastos and the wooden seaffolding, the remains of which allowed Adrasto to build the wa rder's house ,

and they \Vere plaeed in position - the last oue at a height of 36 metres -to eonstitute the monument that Theodosius and Areadius reproduced in a duplieate in Byzantium.

lt is an extraordinary pile of stones. The maehines used to plaee them were far more eomplieated than the structure that was built with them. Oistinguished monuments , the first representa tive of the empire in expansion and the second one of the empire in defenee. 8ut they are mereIy piles of stones simply placed OIle on top of the other as in prehistorie dolmens. The engincers and arehitects of today, we could indeed say the descendants (the <lrtist.ie heirs) of Apollodurus, diseover a disarming elementariness in t.he struct.ure of these monuments. The Romans were able to do (ar more: the great thermae bear witness to this.

F'urLhermore, the Syrian designe r of the colunlns had built the bridge over the Dallube, a miracle of engineering, and an example of building technique that rC-arose in the treatise of Rondelet , and he rcpresented it on the first column.

Apollodorus understood theatre, and Trajan 's basilica built by him a few metres from the eolumn was a great edifiee articulated with a complex equilibriull1 of waUs, arehes and trljsses.

And yct. the columll with the spiral rUlllling through its interior up io the t.errace 011 the abacus, and the cella in the hoUow of the stones of the pedest.al , is Like

the shells of certain molJusks that are rounded on the outside anel twisted on the inside, or the llving organisllls that conceal their complex entrails, or more simply like a building whose articulated function s require an organic succession of envirouments. Unlike the monolit.hic obelisks, the column by Apollodorus is

in fad a building, OI' raLheI' a tower. An ambiguous pile of stones.

Que wonders why Apollodorus required sueh cumbersome elcments in order to build his tower How ll1ueh easicr it would ha\'e been to make the walls that

form the hollo\\' cylinder with a c1assical isodomic work, with small, weU dressed

stones that were easy to transport, to lift and to place. The techniqlle of the isodomon even appears several times OH the marble rellefs of Trajan 's Colllmn:

t,he person carrying the block on his back, carrying it up the steps, placing it carefully on top of the waU ... Apollodurus was a master of the art of building

with "small pieces" : machinesof \\'ar and siege towers were his speciality. On the

272 STRUCTURAL ANALYSI$ OF HI$TORICAL CONSTRUCTIONS

death of his emperor, the architect from Damascus composed a treatise on siege

warfare for the successor, the difficult Hadrian, and showed his full capabilities and his genius: "since in battle it is not possible to transport heavy, cumbersome elements, one should be able to make the large structures necessary for laying

siege using small pieces"

The commemorative tower , the support for the illustrated volume that narrates the campaign of Trajan, was not treated with the refined intelligence of the

slender siege towers. Seventeen rocks (p lus the pedestal and the abacus) were laid one on top of the other with a primitive logic to raise the symbol of victory by one hundred feet. The staircase that leads from the cella to the terrace could have been built, in the interior of a normal tower structure, like so many others in the tem pies and thermae, with stones cut in a trapezium and carefully

mounted on the outer waU; instead , it was hollowed out in the stone just as primitive man dug out his cave. But not with the precision of the surveyor , with the exactitude of the astronomer, with the grace of the engraver, without uncertainties in t he gradien t , without errors in the line. The step with which a drum finishes is followed by the step with which the following drum begins, and the staircase continues uninterrupted , the junction unnoticed. Even the narrow slits that illuminate the space have a strict rhythm, with the irreprehensible

nature of the musical instrumento An ineffable pile of rocks, rough alld refined.

And the other tower-columns, whether in Rome or in Byzantium, followed the same design strictly. The only difference is t hat the pedestal of Marcus

Aurelius's Column is three metres higher. Seen from the Via Flaminia (today the Via dei Corso) , once six metres lower than its actuallevel, the column on its pedestal seemed to have a vanishing perspective , totaUy different from that of the column placed by Apollodurus between t he two libraries, inside a courtyard.

Bu t it is not the image that we are discussing here, but t he material, which is the direct work of conservation t hat we wish to undertake. The impressively rising image of Marcus Aurelius's Column no longer exists toclay: surrounded

by houses , in the centre of a square, we see it as domestic, morc similar to the monument of Trajan than to t hat of the victor of t he Germani and the SOo rmo.tians.

2 .· THE STATE OF DAMAGE

Earthquakes, which are such a dramat ic issue today, \Vere not unusual in

antiquity: the reports of Pliny and the treatise by Seneca give plcnty of evidcnce

of this, and the city of Rome suffered many times. In the republican period t he earthquakes of Rome were registered in the annals of t he Pontifices: ct Hastac

A. GUlFFRE I Marcus Aurclius's Column 273

Martis in regia motae"; the cuH of the lances of Mars thus constituted a rough seislTlological observatory . Nor do we lack documents of later periods that show damage and restoration of the monuments of Rome: in 443 AD "ceciderunt statuae et portica noval!, and a series of lesse r damage to the st ructures af the Caliseum . Again in 508 (484?) the consul Decius Marius Venantius repaired

the arena and the podium of the amphitheatre , but in 801 (dimarando Carla Magno in Spoleto) many monuments collapsed) and the art of restoration that we wish to I'ecover today was fo rgotten.

As is customary in seismolagy, we look at the past to predict t he future. In substance we have been able to clarify , taking the motions af a lest by Ignazio Galli , that t he foundation s()i ls of Rome have transmitted (and wiU transm it ) earthquakes from two different and independent seismogenetic arcas: thai af the Colli Albani, the site of t he ancient volcanic activity in the region, for which the maximum intensity recorded in Rome is VII degrecs 011 lhe Mercalli scale, and that of lhe Appenine UlI1bro-Abbruzzese, from L'Aquila to Norcia, that !l ave oftcn produced inlensities of VIII degrees in R,ome .

The mast famous earthquake that has caused damage to Roman monuments

was on September 10 1349, just after the plague and only a fc\\' months before the opening of the Jubilee.

It is difficult to determine the intens ity af that fatal event: it is recounted by Matteo ViUani, and menlion is found af it in a letter of t he Pel rarch . The earthquakc caused serious damage to the Bas ilica d i San Paola i di San Giovann i, anel elemolished "a part of t he noble tawer of the army, and the tower of the Count , leaving in many other parts af Rome the memory a f its ruins" The state af const ruction in Rome 'vas anyth ing but normal: "precarious" situalions were more widespread than the stable ones, and though the narration af Matleo Villani couId suggest a scenario of grade IX or grade VIII , we may consider that the dilapidated state of the buildillgs seriously aggravated the efTccts. The two columns are nat mentioned by the sources: was th is an omission or were

they left unharmed?

Structures of superimposed blocks have a very complex dynamic behaviour: their seismic stability is quite different from that of monolithic obelisks . Beyand

a certain threshold of acceleration , the latter begin to oscillale 011 their base due ta the groulld motions; only at far higher (but not ver)' predictable )

leveIs of accelerat ion thall t his t hreshold do they lose their equil ibri um and

collapse. Block system s are alsa set into motion beyand the same threshold o f acceleration , and they can a lso withstand far higher accelerations than those

that trigger the motioIl, but the oscillations produced by the earthquake fila)'

274 STRUCTURAL ANALYS IS OF HISTORICAL CONSTRUCTIONS

cause t.hc shifting OI' rotation of the individual e1ement.s ,sy lnptollls Ihal cO l ne

before the collapse. F'urthermore, the frequ ency of these oscillations does 110t

depend on 1.hc eharacteris1.ics of 1.he materi ais but on t.h~· amplit.ude of t.he

1l10t.ion: the more the mOllolith or column leans away from lhe vertica l, t he

lower is 1.he frequency with which it oseillates . T hc "prope r perioel of vibration"

of this st.ructure ea llllot be dcfined as for elastic structu res, evell if a phase of e1astic dynalll ics can be detected duc to vcry sll1all el ynamic excit at.ions that do

1101. involve the opening of t he join ts.

Severa! cxperimcnts have been attempted on 1l10dels of t,he column in order to

clarify this behaviour, anel numerical analyses and other studies are underway,

though the results are as yet incollclusive.

The resistance of such st ructu res to earthquakes is particula.r1y high, but difficul t

to evaluate. We can predict the value of acceleration of t,he ground that puts

into motion t,he sys tem of drull1s , anel we know tbat in orner to J"('ach collapsc

it is neccssary for t he syst.em to show peaks of acceleratioll that are fa r higher

than this value, bu t we do no1. know how much higher. Usually, t,he crossing of this threshold Icaves irreversible signs on the strllcture: shifiing af t he drums

OI' chippillg of the edges where the rotatiol1 is concent rated: these are the

unequ ivocal sings of seis mie stress . Thc fortuitousuess of the motions trigge red

by carthquakes does Bot aUo\\' us to make quantitative forecasts Oll the dcgree

of these dislocations: they grow with thc value of the peak acceleration but also

with the number of peaks at which thc accelcratioll goes beyond the threshold value, and we do not know how.

An inexplicablc , dist urbing piles of blo cks !

Toda)' both the ROlllan columns show sueI! signs: displacement and rotaiion can

be secn bet.ween the blocks, but. to a different extent in the two spccimens. The

Trajan 's Column only shows chipping, a c1ear sign of a tilting motion that has

concent r ated the weight of the overhanging portion 011 one edge of the drum ,

and in another p osition a displacement of a fe\\' millimctres. Here and there we

can find vertical damage affecting the whole height, of a block and crossing the t hickness af Lhe eyl.indrieal waU.

Marcus A urdius's Column is badly damagcd: elisplaeements of more than I Ocm,

vertical damage going through aU the elrums (except for one, the tenth), two

of them running from the base to medium height. Domenico Fontana, \Vho

restored it il1 1590, had to say that it "was ready to coUapse" .

Something of the state in which Fontana found Mareus Aurelius's Column

A. GUIFFRE' Marcus Aurelius's Column 275

could be gathered from the different prints that were made of it before that

time, but far more appeared when a young student, Marco Pelletti, staying for a few months as a stylite on the scaffolding of the column, first under the

auspices of the Archeological Ser vice and then to carry out his doctoral thesis

in architecture, removed all sigos, alI cracks, ali sutures .

In the secolltllialf uf the ei.ghti.e:., archi.tecb, e llgiueers, lIIechanics, archeolugists,

and surveyors worked with remarkable fervor Oll the Columl1 together with the

architect GianGiacomo Martines, who directed the restoration works for the

Archeologieal Service.

The first result of this incredible survey is the comparison between the old

prints, which showed the column split into two zones, and the map of the

inserts placed by Fontana in order to make it good; the second is the system of vertical fractures that brcak t he monolithicity of blocks and transform the

work into a set of "smaU pieccs". Just what Apollodurus had avoided at the

cost of enormous effort.

We have already observed, running through the unforgettable scaffolding of

the eighties, that the most spectacular dislocations affect only portions of

blocks, fragments included between the aforemcntioned transverse damage that

\Vere pushed outward by the seismie 1I10tioll while the main part of the block

maintained its contad with the underlying piece. Only block No. 10 has

undergone a complete displacement, dragging with it thc part of the column t.hat

is above it, and the survey of the dislocations has made it possible to determine

the mechauism associated with this, which shows that the column could easily

have collapsed. The two vertical fractures t1lat start from the two major cracks

and [Ull to the base have isolated a pilastrino alld ou this t,he portion of the

column from the tenth block upwards supported itself momentarilYl pushing it autwards.

But why this dreadful panor.uua of fractures?

A hypothesis comes to minei spont.aneously: before the earthquake upset the general order of the column (in fad it is a very tragic premi se that the

earthquake could have damaged the structure to sueh an extent) lightning could

have caused the two la.rge cracks t.hat are reproduccd in the prints af Giovanni

Antonio Oosio, Marco Sadelcr and Enea Vico, and t ha.t were recognized by

fvlarco Pellett.i behind the inserts of the Fontana. It would thus also have been

responsible for the vertical fraciures that run from the cracks to the base of

the column, br~aking the blocks iuto parts. In fad this situatioll of fissures

is typical of waU structures hit by electrical discharge. Arcadius's Column in

276 STRUCTURAL ANALYSIS DF J-lISTDRICAL CONSTRUCTIONS

Constantinople, surveyed by Gyllius in the middle of t he 16th century, showed

similar vertical fradures: the lightning had hit it on June 24, 550 and the fracture was contained by means of aspiraI of iron hoops around the Iower

drums . The vertical fracture produced by the lightning on a brick chimney is

documented by a photograph reproduced by Donghi in his Manual. 11 Poleni describes the cracks in the bell-tower of San Marco that occurred on April 23, 1745 The effects of lightning on ancient m onuments of Rome have been recognized ou other occasions : a collapse in the basiIica of San Paolo in 443 was attributed to Iightning by R . Krautheimer , and the obelisk of Piazza del

PopoIo was rccently damaged due to similar atmospherie p henomena.

Furthermore, in more rccent times reports of lightn ing striking Marcus Aurelius's Column are not lacking: 12 August 1679, Avviso di Roma, "a thunderbolt hit Marcus AureIius's Column in Piazza Colonna" and damaged the sculpture; 22 September 1841, "at around nine thirty .. lightlling having hit the Column of our piazza has damaged its vast reliefs"

But together with the two main vertical lesions that suggest the wrath of Jove, the fissured panorama of Marcus Aurelius's Column shows a diffuse series of other fradures that fragment the mOllolithicity of the blocks, similar to the ones that are found in lesser number OH Trajan's Colmon. lt is known that marble taken from the quarry and worked tellds to crack. The pedestal of Trajan's Column shows such fissures, but they may also appear in time whell the block has been worked to a small thickness, as for the circular waU of the tower, and in this case the cracks become authentic fradures. Perhaps the blocks used for the monument of Marcus Aurelius were cut from a more fragile vein than those cut for Trajan's Column. Bui the earthquakes could also have fract.ured the drums: a slight defed in the planarity of ihe çontad can cause a fradure when the oscillation leads the weight of the column to be applied 011

the edge sedor.

However, thus damaged, with the monolithism of the blocks broken , Marcus Aurelius's Column could have seemed to be in a reasonable state of repair to ihe observer: fissures have always accom panied tbe panorama of waU structures. But this incoherellt assembly was in sueh poor state that the earthquake could

easily destroy its integrity.

Was it clairvoyance or seismic science that led Apollodurus to not spare

prisoners' shoulders to pile up giant, monolithic blocks of stone, rather than

cOllstructing the walls with t he ephemeral technique that he used in the military campaigns? Trajan 's Column, evidently saved from the lightning, only suffered

the chipping mentioned above as a result of the earthquake. Most of the drums

A. GUIFFRE I Marcus Aure1ius's CoJumn 277

are complete and only in one, in which we note two vertical fractures that isolate

a portion of the block, do we observe a small displacement, a partial dislocation.

~1arcus Aurelius's Column would havc beco saved írom the earthquake, like

Trajan 's Columo , if it had not been previously fractured.

Recent studies of the foundation soils of Rome leave no doubt about whether the location of Marcus Aurelius 's Column couId be the si te of an amplified

seismic action A large port ion of the urban surface, alongside the Tiber lies on the alluvial basin of t he river , and this is where Marcus Aurelius's Column is locatcd1 whereas Trajan's Column stands on firmer ground outside the edge

of the basin. It is therefore definitely possible that the two coIurnns suffered the earthquakes of Rome with different intensities. Or rather , it is definitely possible that Trajan's Column, placed in a firmer location than that on which the greatcr part of the city was built , suffered lesse r seismic actions than those that caused grade VIII damage to the urban buildings.

Marcus Aurelius's Column is certainly more damaged , but what effect could a grade VI II earthquake have 00 th is haughty pile of blocks?

Although the quoted studies on the nature of the foundati ons soi ls aliow us to foresee the presence of low frequencies in the seismic motion of the aUu vial basin 011 which Marcus Aurelius's Column is located, recent experiments con firm that these frequell cies are flot sufficient to break up an organic whole of complete blocks. However , a stronger dynamic action than that suffered by Trajan 1s Column would 1I0t have produced in a. column that was stiU whole the typical

vert. ical fraciures caused by üghtlling, but instead chipping 01' general shifting betwcen Lhe blocks, signs that always characLerize the effects of earLhquakes on such struciures .

Certainly, wc do not have documents that state ho", t he cracks in the marble that wc see were caused, we have no documentary evidence of the appearance

of the cracks and t he vertical fractures that. are typical of lightning, and we have no documents that state how the earthquake discollnected the fractured drums that were replaced by Domenico Fontana. Vve can onl)' put forward a hypothes is that we consider to be reasonable.

PersonaUy, wc are inclined to state that the great.er damage sufl"ered by Marcus

Aurelius's Column than by Trajan 's Column is not due to ali earthquake of a greater intensity (though we do agree that it cauld have been of a greater

intcnsity ) but to the fraciures that ran through the blocks.

278 STRUCTURAL ANALYSIS OF HISTO RICAL CONSTRUCTIONS

T his statement is not without consequcll ces , as we will see, on the future of t he

column, or at least on our aHitude towarels the future of the column.

3.- T H E R ESTORAT I ON BY F O NTA NA

It was perhaps the earthquake of 1349 that maele the fissureel blocks collapse. We are forecel to base the hypothesis 011 well -known events: the ollly previous earthquake recorded was that of the begiuning of the 9th eentury , which was certainly very se rious , but how could the colurnn have supporteel the second one if it had already beclI seriously damaged by the first?

Fontana undertook the restoration for Sixtus V , and fi nished it in 1589. His intention was to restore the column to its or iginal splendour. He filled the cracks with new pieces of marbJe and on the new surface he had scenes of war sculpted in imitation of t hose that had been int.errupted by the gaps. According to him

(and we have no reason to doubt his worel ), many portions of marble stood out a paim anel a half from the column , anel hc had to reinsert them using levers anel winches . He was not always successful: Marco Pelletti locateel some pieces of the original marble on which the bas- relief shows the same 15th- century technique as the added portions. Unable to reacljust the protruding pieces the Fontana decided to recarve that stone eliminating the protrueling part , so the thickness of the cylindrieal walI at that point was reduced to only 30 em. The redudion in thickness, though not 50 serious, is general: the internai surface of the hollow eylinder, whieh delimits the spi ral , was recut to remove the steps resulting from the dislocation of t he pieees pushed outward by the seismic movement. Thus, the dislocations go unobserved for the visitor who goes up the spira l staircase. Even in the interior lhe 15th-century restoration restored t he column to its original appearance.

Fontana completed the work by inserting a great number of metal b races to conned the aelded anel relocated pieees.

lIow are we to judge the L:UlTeut statc of the st ru cture? lt is true that the

introduction of the missing pieees has provided points of support tha t are indispensable to the strength , anel that the replacement of t.hose that had been shifted has returned the strudure to how it was before the ea.rthquake almost destroyed it completely: apparently whole hllt. seriollsly fra.ct ured. The

llllmerous metal cramps with which Fontana united t.he edges of thc fract.lIres

havc to a eertain l'xtent restorcd the continuity of caeh bloek.

Aftcr F'ontana's rcstoration of the column , it su ffered the earthqllake of 1703 ,

A. GUIFFRE I Marcus Aurelius's Colurnn 279

which was famous beca use it was 50 destructive in VAquila and in Norcia (it

was obviously the same seismogenetic mechanisIll that. had causcd t he olle in 1349) and because the damage it caused to the areade of the Coliscull1 is often ment.ioned. In fact , however , its effects were BOt. so serious in Rome. An eartbquake was also report.ed in 1812, whose effects ou t.he Coliseum Icd lhe aulhorities to commission the restoration by Stern, but this alie was also fIot seri ous. In substancc the rest.ored columll has not yet 8u ffe rcd a ::Icrio tl s tcst of

it.s integrity, and we do not know what would become of it in ali eartbquake

like that Df 1349.

To conc\ude: if ollr hypothesis is accepted, that is, that the COI UIllIl was sc riously fissured before the mediaeval earthquake, and 1 his earthquake did no more than break up the fragments, it can bc observed that in cOll1parison with then the column has today a few cracks less and a few braces more; its condition is beBer

but the state of fi ssur ing its substantially the same.

If our hypothes is is not accepted, anel it is believed thaL it was the 1349 earthquake that fractured the column anel reduced it to the state in which Fontana found it, it musl be agreed that today the column is in a dramatically more vulnerable slate thall it was before that evcnt, of which WI> fear the returno

\<\Te cannot look at this uncertain, precarious pile of blocks without a certain

anxiety.

Fontana was a technician of great repute. and it is indeed not necessary to quote

the occasiolls on which hc had the opportunity to delllollstrate this. However , his work on the COIUIllII, in oue way or in another, follows a logic that we would

not repeat today.

Let us reconsider his work on the column: his valuable repairs, the re.assembly of the disconnected pieces, the clamps holding together lhe fissures.

Let us first state that today we are forceel to admit that we are unequal to

lhe task of large wall caost ructionsi there is 110 modern architect ar engioeer who would have the courage to undertake a project \\'ith the same structural

solutions as t.he large wali structures of the past, made of stone or brick. Today we do not depend OIl our knowledgc of building, as did Domenico Fontana,

hut on the respollse of the mechanical models with which we schematize the structure. Anel when we lack the mecharucal l110dels and the corresponding

algorithms as a basis for the construction of the waU , we are helpless.

The structure of the column, as we have already said, is elementary but

280 STRUCTURAL ANALYS1$ OF HISTOR1CAL CONSTRUCflONS

mechanically complex: the response of the models that we have beeo able to

formulate - and only in the last few years - is imprecise. The modern engineer, who anyway does not know the most up-to-date models, would not think twice

about perforating lhe marble from top to boUom and inserting metal bars to

fonu a vertical reinforcement through the whole height of the column. In this way it would be possible to borrow the model that we use for reinforced concrete structures and to estimate - correctly ar incorrectly - a Ilumerical answer.

The choice of Apollodurus , singula.r, ineffablc, disquieting, would lose its meaning.

Indeed, an engineer whose name has not been passed down did not think twice about it. In the restoration programme of the 1950's it was planned to insert four vertical metal bars, of which fortunately no trace is to be found: a sensible superintendant was able to prevent the boring.

Today, and real1y Iam referring to the last three or four years , it is beginning to be recognized that the mechanical basis of the structures of a period, even if not yet formulated, exist and justify (and how could they not justify?) the century­long duration of these works. There follows the equally obvious consequence that in this new light modem restoration work aims to avoid disturbing the iutrinsic mechan.ics of the architecture of the past.

But this is not enough: the buildillg customs of a period have a cultural siguifi call cc that is totalJy equivalent. to their formal sensibility. It could perhaps be added that without an understanding of thcse customs, the work of conservation that now , at the end of the millenllium, has been recoguized as

being the indispensable legacy to pass on to the next millenuium cannot but be blind and disfiguring. As in fad it was from the postwar period onwards, and is still , due to the cultural inertia that inconceivably characterizcs this sedor.

The mechanical choice of Apollodurus, to build the column as a pile of blocks, sllould no" be undervalned. Its efficacy against earthquakes has today been demollstrated by modem algorithms. Though these have not yet reached the point of making a fnll evaluation of the resistance, it has been observed with stupour in the spectacular experiments 00 the vibrating table. BuL this had already been demonstrated by Trajan's Column: it is unharmed due to intrinsic mechanical ()11ality, rather than due to the a1.tcnuating: virj,ue of its subsoil.

Fontana did 110t appreciate, coulcl not appreciate , the significance of the great

blocks. Por him the column was a tower: a circular walI that was original1y three palms thick with in its interior aspirai sta.ircase l.ike the a li e of the Vatican Dome

A. GUIFFRE I Marcus Aurelius's Column 281

which was completed in the same year.

Anel the circular structu re that Fontana saw in Marcus Aurelius's Columll ,

50 minute1y fractured , was truly a \VaU. He thus fiUed the gaps as if he

were restoring a walJ , by inserting the stones without paying attention to the

origiual positio ns of the drums, without worrying that the inserts straclelled the superilllposed blocks and nega.tcd thcir individuali ty.

Today we woulel not do this. We woulel not do it because the mechanics of Lhe

structurcs of s uperimposed blocks has a possiblc , though not yet exhaustivc,

formulation when the surfaces of contact are Hat . But above ali we would not

do it for the sirnple anel incontrovertiblc reason that Apollodurus wauld Hot have

done it. Apolloduru s piled the blocks one Otl top of t he othe r, with pe rfectly

planed col1tact surfaces, ensuring the hori zontality with the precision of the

plumb-linc , each drum bcing a condit,ion for the laying of the following oue. If t he drums are fracturcd , we must repair them as far as possiblc , 110t glue them

togcthe r or eugagc thclII with each other .

lf we had Lo carry ou t today Lhe rcstoration that Domenico Fontana concluded

in 1590 we wauld fill the gaps in each drum with stones cu t so as to adhere

to the fra.ctured edges, restoring the integrity of the block whilst. respeding its

original geometry. We would be preparcd to glue the new stolles to the edges of j he old ones with tongh resiu s, always respccting the individuality a f the

individual drum. We on ly need the chcll1ists t.o assure us that 50 years from

1I0W the glues wiU not lose t heir effect iveuess, anel that. they wiU !lot becotne

cviden., thus disruptillg the appearance like the iron placed by Balanoz in the thirties bet.weell the marble blocks of t.!te Acropolis of Athens.

T he beUer we are at gluing the pieces together , the more we will retum t he

co!urnn to it s original state that C i111 be seen in Trajan 's COIUIllI1.

But toda)' wc must not repeat the restaratioll af Oomenico Fontana, which is

also the objcct of collscrvatioll. It is t,herdore necessary to follow othcr roads.

4.- PROPOSAL FOR AN ANTI-SEISMIC RESTORANTION

In an ideal temporal vicw, Marcus Aure Lius's Colurnn represents the present ,

Trajall 's Calurnn the past, and Arcadius's Column an undesired but possible

future.

Trajan's Colum n is in fad in the state in which Marcus Aurelius's Colull1l\

282 STRUCTURAL ANALYSIS OF HISTORICAL CONSTRUCTIONS

was before "something" reduced it to the st.üe tha! allowed the earthquakc to

devastate it. In this stale Arcadius's Column remained for a long time, but success ive earthquakes led it to the state fram which it was mercifuUy saved by

the demoHshers in 1717.

Today Marcus Aurelius's Column is halfway bctween these two positions.

The restoration by Fontana, we observed, does n01 resolve the precariousness

iníroduced by the fi ssuring that split almos! ali the drum s af the column . A serious earthquake would find the structure no longer constituted) as it originally was, af large su perimposed blocks, bui af small pieces that are only weakly

connected by metal braccs. And what is more , with the two unfortunate paraUel fissures that isolate a vertical portioJl of the externai waU from the tenth block

to the ground.

Fontana's braces may be effective to avoid the smaU disconnections in the higher

blocks, which are the result of smaU eartl! motions but they cannot restrain the mechanism that has aUowed the tenth block to move outwards, and almost to coUapse. The braces fastened from the exterior beco me disconnected easily if a tilting motiOll comes in to actiou.

Ao earthquake like the one that devastated the column wauld toclay finei it a little more in order, and perhaps it would devastate it less, but a serious earthquake is always a threat. Anel ir the new earthquake did 110t cause the collapse, it could lead the column to a similar state of collapse that. leel to the demolition af Arcadius's Column .

Therefare, if we wish ta avaid the Cuture represented by the monument of Arcadius we must at Ieast prevent the mechanism triggereel of[ in 1349 from being reactivated.

Arcadius's Colurnn was secured with a spirai iron hoop írom outsidc, a disfiguring but effective intervention. Wc can fallow this examplc warking on the interior .

Let us imaging a metal spi ral that runs along the internai waU of the tower

follawing the graclient af the staircase, in fact a clouble spiral cOllstitutcd of two bars of titanium placed over and under t he staircase, against the internaI

surface af the \VaU. These bars cross aU the ffactures that split the blocks anel

in correspondence of each of the fractures a fine pin , conuectecl to the spiral through the thicknes~ of the wall anel with a hook a few celltimetres long, secures

lhe twa eclges af the fracture from the outsicle. All the fragments are thus linked

A. GU IFFRE I Marcus Aurelius's Column 283

to a continuous structure which conneets them to each other from the inside. It is no langer possible for ane af the pieces to be projected outwards leaving the adjacent pieces in their place. That is to say, a significant degree of solidarity

is achieved that improves the overall behaviour greatly. The externaI hooks are small , and they will secure the sculpted stone by means af bronze plates

that make a continuous contact of maximum effectiveness without affecting the marble.

The only drawback of this intervention is the continuity of the spiraI through the drums. This cont inuity must be interrupted at each level. The metal bar will t herefore be cut at each joint bet ween d rum and drum, t hough its fun ction as a connective e1ement is fully maintained.

5.- CONCLUSIONS

It is hardly necessary to state that the propasal described above is only a criterion , an approach to use in order to resume the studies that were interrupted at the end of t he 80s, and with the same attention to start to evaluate from t he ins ide of t he column the exact positiou of the proposed metal connectors. But in conclusion, we must again consider , in the light of the intervention, the dilemma of the cause of the damage found by Fontana.

If on September 10 1340 the earlhquake found Marcus A urelius's Column whole as it was in the original project of ApoUodurus, and with its violence amplified by the soft alluvium, and with the frequeney of its peaks of aeceleration , it shook and broke the column so much that it threatened its overalI in teg rity, then our p roposal is absolutely useless. Doe ar two metal bars, scrupulously connected

to ali the fragments of rocks t hat we today find in this tragic Aotonioe mosaic, are very far from reconstituting the lost monoüthicity. And if the earthquake once shook and broke the columo wheu it was in perfect conditioll , it wiII totally demolish today's column , despite our titanium spirals .

If it were true that the earthquake that hit Rome shor tly after the epidemic of t he plague found Marcus Aurelius's Column healthy a nd after a few seconds left

it in ruins ) today we would have no hope for the column: we eannot stop the earthqu ake. A healthy economic policy would advise avoiding expenditure on

useless restoration works, and would limi t the care to a periodical cleaning. A healthy policy of civil protection would dose the square on which the fragments

of the crowning glory of the philosopher emperor would be t hro"'lI.

284 STRUCTURAL ANALYSIS OF HISTO RICAL CONST RUCT IONS

Bul \vc do no! bclicvc that lhe eart.bquake is capahlc of so much , despite

lhe amplifications anel lhe harmful frc quencics thai lhe floods af lhe T iber

confe r OIl it j we do 11 0l be lieve that OH lhe day before lhe J ub ilec p roclaimcd

by Clcment. VI the gloriou.'; pile af blocks assembled hy the emperor Marcus

Aurelius Anloninus was u nexpcctcdly t. rall sfonned into a p recar ious pile af

s toncs. No, it had becl\ al ready u ndermined by previous a ccidents, even by prc\' ious earthquakes. Only bccause af thi s substantial degradat ion could lhe

cart,hquakc ove /' comc it. in its fragmclLt.ed statc.

Anel no\V, ir WI:' takc st.cps to mitigatc th is statc a f degradat ioll, ir wc restore

some af its for mer in teg rity, ir we contraI lhe weak point. frorn t he tenth drum

dowlI t.o t.he ha.se which threatcns iL s st.abi lity\ Wl:.' call havc good hopes for its

fuiUl'e a nd cxorcise the spcctres of Arcadius .

In th is case, a hcal t hy po licy of wllservatioll of the cultural heritage should

ta,ke prornpt adion to p ut into pr;tctice t lle experielltes ilm! rcftcctions gai ncd

ill the 80s. At Lhai time , lhe collHlln, covcn'd ill scaffo lding: \Vas sub jeded to

a t.horougb st.udy ihat. cO ll s idcrec! a li ii5 as pects, ali it.s frag lllcnt5, it5 efrective

consis tcn cc, the realily o f iis stOTlCS and t,h eir posi t ions, lhe ll1ech;~nisllls of

dalllagc <:\ lld l he possibil ity of it bcillg rl' p e ;~ted . EilCh sy lJlptom was considered ,

cach picce of infonll;tt. ioll wa.s corrdaicd , in order to rdivc the particular

Odyssey of thi:> colullln .

A. GUIFFRE I Marcus Aurclius's Column 285

NOTES ANO REFERENCES

1.- Giangiocomo Martines, La struttura deU a Colonna Traiana: un 'esercitazione di

meccanica alessandrina , in " Prospe ttiva" N032 , January 1983.

2.- A literary homagc to Marcus Aureli us tltrough the custodian of the column

appointed by Septimus Severus is in : Mana Teresa GlUJfre , La veglia di Adrasta, Ed .

Studia Tes i, Pordenone 1986.

3.- Antonino Giuffre - Fabio Ortolani , Le colonne coclidi testimoni dei l erremoti di

Roma, in A. Giuffre, r ... tomunenti e Terremoti : aspett i statici dei restauro, rvlultigrafica

editri ce, Rome 1988. pp. 55-64.

4.- ApoUodore de Damas, Les Poliorcét iques, in "Revue d 'études greques" 1890, pp.

230-281, translation by E. Lacosl e ofthe text published by M. C. Wescher (Paris 18Gi).

The following passage is significant : C'est ainsi qu 'on peut , avec un petit nombre de

pieces de bois de faibl es di mensions, faíre une grande tour, d 'une hauleur égale à cell e

du rempart ; .. p. 261.

5.- For lhis reason lhe drawing a f Marcus Aurelius's COl tllnJl shows a sl.i ght variation

from Trajan's Column: the tapering between the first and the Jast drum, whkh can be

noled in the founder column, is highly reduced in lhe second : it is a correction of the

effect of perspective produced by the view frotll the base.

6.- Palumbo A. L'osc illazione delle lance de Marte: metafora o rudimentale rilevatore

di scosse?, in Guidoboni E. (ed.), I terrimot i prima dei Mille , Istituto Nazionale di

Geofis ica, Ed . SGA Stor ia- Geofi sica-Ambiente , Bologna 1989, pp. 122-123.

i.- Catalogo delle epigrafi latine r iguardanti i terremot i, in Guidoboni E. (de.), op. cit .,

p. 148

8.- Antonino Giuffre, I Terremoti di Roma, in Giu frr e A., Monumenti e terremoti :

aspetti statici dei restauro, Multigrafica Editrice, Rome 1988, pp. 47-54.

9.- Ignazio GaUi. I terremot i nel Lazio , Stab. Tip . "P io 5tracca" , VeUetr i 1906. An

essa)' by Rodolfo Lanciani , Segui di terremoti neglj edifiz i di Roma antica , in Bullettino

della Conuniss ione Archeologi ca Comunale, Rame 1917 , was also af great u tilit)' in the

study of Roman earthquakes.

10.- The most important dates are: 801 , 897(?), 1349, 1703. On this argument see

also: Diego I\!lol.in and Emanuela Guidoboni : Effetto font i effetto monwnenti a Roma:

j terremoi t dall 'antichità a Roma, in Guidoboni E (ed.) op. cito pp. 194-223.

286 STRUCTURAL ANALYSIS OF HISTORICAL CONSTRUCTIONS

11.- It is often called "the earthquake af Petrarch" , who wrote af it in several letters

providing indications af the whole that agree with those recorrled by Matteo Villani ;

Francesco Petrarca , Familiares , Book XI , Lett . VII (f tom Piacenza, 11 June 1351).

12.- Matteo ViUani in: Muratorius , Rerum Italicarum Scriptores , vol. XIV vaI. 46.B .

A di scussion on the difference between the VIII and the IX degree af the MCS scale is

found in:

13.- Giuffre A., Vulnerability af historical cities in seisrnic areas and conservat ion

criteria , in Proceedings af the congress "Terremoti e Civiltà Abitative", Reme 1993 , in

print .

14 .- Renato Masian i, Seismic assessment af ohelisks and columns, in Structural

Conservation af stone masonry, International Technical Conference, Athens 1989,

l CCROM, Rome 1990, pp . 165 , 172.

15.· For a prismatic solid the acceleration caused by the start of the earthquake is

a / g= S/ H, where S is the minimum dimension of the base and H the height .

16.· For a useful review of the state of the art af thi s argument , see: Ugo Andreaus and

Giuliano Augusti , Meccanica delle colonne e delle costruzioru a bloccru lapidei : stato e

prospettive degli studi , in Pact 32, 1991, "Paes tum . étude de cas de vulnérabilité du

patrimoine" edited by Giuliana Tocco Sciarelli , pp. 67, 126 .

17 .' In a well·known experiment, if an object resting on a flat surface is tilted and then

released, it fir st osciIlates slowly and then with increasing frequency ul\til it stops.

18.· A review of the experimental work carried out in the Laboratory of the Department

of Structural Engineering and Geotechnics of the "La Sapienza" University of Rome,

and a debate on the problem of the mechanical similarity of scale mo deIs in the sector

of structures composed of blocks can be fOruld in: Giuffre A:, Studies in progress on

the seiSrnlC behaviour of the imperial columns in Rome, Rapporto N 5, 1986.

, 9.· Sec:ret Vati ca.n archive - Arehivium Areis Armatio B3 - Libro di tutta la spesa

fatta da N.S. Papa Sisto V aUa colonna Antonina e Traiana; transcription by OrneIla

Sforza and Maria Vittoria Zaccheo for the Archeological Superintendance of Rome,

1984.

20.· Marco PeUetti was comntissianed by the Areheological Superintendance af Rome

to study the marble inserts by Fontana in the monument o He then devoted rurnseLf

to rus dadoral thesis, studying , interpreting and drawing aU the di slocations in

correspondenee with the fractures , starting from the base and slawly reconstructing

A. GUIFFRE I Marcus Aurclius's Column 287

the current configuration of the column. The rapporteur, the author of these notes,

informed rum at the beginning of the purpose of the unusual survey alld finaUy, on

March 21 1989, presented the astonisrung but unequivocal results to the Doctorate

Commission. The survey by Marco PelleUi is tota11y different from the one carried out

by Piranesi, whom the Romans saw for months hanging in a basket on the side of the

colurnn . In the 17th century the figures of the bas-relief were studied wtih great care,

but in 1989 attentian focussed on the constructlOnal aspects and the reqtti rement of

restoration. Establisrung whether the fissUIes betweell two blocks were caused by the

movement of one ar of the other , or of both, requires the same attention and the same

extension a f the field of observat ion that Marco Pelletti must have used to distinguish

the 15th century scultpure of Sitia Longa from the imperial one.

21.· See the entry "Colonna di Arcadio" in the E.A.A. (Treccani) . Dongh.i O., Manuale

dell 'Architetto (1906). Appendix , chapter on "Sicurezza dei Fabbricatj", B, p. 128,

Turin , reprinted 1935.

22 .- Poleni G. , Memorie Istoriche della Gran Cupola dei Tempio Vaticano, Padua 1748 ,

Book I, Chap. XIV "DeUe cause esterne de' danni neUe fabbriche ; 125, co l. 75: "n primo urto deI fulmine feri I'angolo posto verso Scirocco Levante .. Ma.. veniremo ai

gran colpo di quel fulmine neU 'angolo .. verso I'orologio, ... nella quale cantonata il

fulmin e fece una terribile squarciatura .. estendendos i in una lunghezza per pendi colare

non minore di piedi veneti novanta". Also in the bell -tower of San Marco lhe lightning

had two areas of impact and produced cracks that were prolonged vertically towards

the base. which refers to the Liber Pontifi cares (I, 239), see Guidoboni E. (ed.), op.

cit ., pp. 201.

23.- For these quotes see Romano P.: La ColorUla di Marco Aurelio, in L'Urbe , Rome

[955.

24 .- An in-depth study of the surface variability of the se ismic movement in the cit)' of

Rome has beeo carri ed out by A. Rovellj , D. Molin , L. 1hlagnini, A. Caserta, Variability

of elamage pattern in Rome: combination of SQu rce anel local effects, presented to the

5th lnternat ional COlúerence on Seismic Zooation , Nice 1995.

25.-A later stud)' explicitly addressing the effects af the ea rthquake on the two calumns

(though we are in partial disagreement \\'ith it) is E. Boschi (et al.), Resonance of

Subsurface Sediments: an Unforeseen Complication for Designers of Romao Colwnns,

Bulletin of the Seismological Society of America , Vol. 85, N01, Feb. 1995 , pp. 320·324.

26 .- A very recent experiment being developed with the IZIIS laboratory of Skopje 0 0

the initiative of the ltaüan Ist ituto Nazionale di Geofisica has shown that the se ismic

actioll may produce the crosswise fractures that split the blocks The model const ructed

288 STRUCTURAL ANALYSIS OF HISTORICAL CONSTR UCTIONS

on a sca le a f 1:6 with a material tha1 reprodu ces Lhe charact eristi cs a f lhe marble at

a reduced scale \\Ias submitted lo very violent dy namic actions up l o accelerations a f

0.2g, with variations in lhe frequency content a f lhe t es t accelerogralll 50 as t o foUow

lhe frequencies af osciUat ion af lhe column . Several crosswise fradures appeared in lhe

blocks, but no vertical ones and never more than two per block. These were facilitated

by defec t s a f fiatness in lhe contact between lhe blocks, bllt aft er 3nother ten slresses

that caused violcnt opening af the joints, and di splacement a f lhe t op that taken to lhe

scale a f lhe m onument rcached 70 em , the model remained intact , as Trajan 's Column

is t oday : with some chipping , with crosswise fractures in the blocks, with a general

di splacement in lhe eleventh block , but without the devastation that characterized

Marcus Aurelius's Column whcn Fontana b egan t o res t ore it.

28.- The di splacemeuts between lhe rocks of lhe frotlt columns af t he Eretteo of the

Acropoli s in At hcns and in lhe Parthenon produced by lhe eart hquake of . are well­

knowll , and the studi es of dynamics confirm t he ari sing of t his mechanism as an etrect

of seism ic action .

29.- However , we canuot but agree O ll the fact that the fluvial basin , certainly lhe reason

for the amplifi cation af lhe seismic m ovement , transmitted it with a. freQuency content

that was capable of causing the resonancc of the cohunn for the follawing reasons: a )

the cllaracteri sti c frequellcies af a basin ma.y be shown only by direct experimcntation

caused by the earthquake, as happened in Mexico City, anel not by numeri cal calculation

that does not take into account the complexity of local conditions; but even whcn we

place our faith in these fa recasts (illdeed there are experiment.al dat.a th3t confirm

these result s), thi s second reason cann ot be ovcrloookeel ; b) t.he column composed of

drums is very far from having an elasti c b ehavíol1f : the stronger lhe seismíc actíon

is, anel lhe m ore il pra du ces oscillations that opell lhe joínt s between t.he blocks, lhe

lower the frequency of response is and lhe dynami c behaviour m oves away from lhe

resonance. It can in 110 way be attempled to predi ct a rcsp onse wi t h eval uations cf the

resonance. The frequency that is measured as au efrect of vcry slight en vironmental

actions (linked t o the characteristi cs of lhe material and t o l he nal ure c f t he land

0 11 which the foundation rest s) has notlting to do wit h the frequency of t he strong

osci llations that however depend on lhe geometry of lhe column aurl ou the amplitude

cf t he di splacement . Hcwever , it i5 truc that thc low frcqucncics that wcre presenl in

the site of Marcus Aurelius 's COIUIllll and not in that of Trajan 's Column increase lhe

responsc lo some extenl .

30.- Since the earthquake af 801 secms to have been of considerable intensíty, our

illuslration could lead us to sustain that on that dat e Marcus Aurelius's Column was

t ruly wholc, like that ofTrajan , and the occasion that shattered the blocks was betwecn

801 anel 1349.

A. GUIFFRÍ I Marcus Aurelius's Column 289

31.- Plundering what remained of the Setlizoruo.

32 .- The damage to the Colli seurn reported 0 11 Ih is occasion , ofl en quoted , shows the

terrible st ate a f lhe masonry ralher t han l he violence a f lhe earthquake. On another

accasiol1 , in the mid- I ilh century, there are reports a f collapses in the Colli sewn , but

no mention is made a f earthquakes: l he coHapses tberefore occurred spontaneously or

dlle to plundering . See Emanuela GuidobOlÚ , op. cit.

3.- They have al ready played this role in earthquakes subsequent to ! 590, earthquakes

that though weak cauld not bul contain the dangerous frequencies revealed by the

schalars af the lstituta Naz ionale di Geofisica .