Frank Willer, Roland Schwab & Kati Bott

Large Roman Bronze statues from the UNESCO World Heritage

Summary Introduction

Fragmented bronze sculpture is an important category One of the important categories of finds from the Roman of finds from the provinces in the north of the Alps at provinces between the north of the Alps and the the frontier of the . Portraits and statues North See are large roman bronze sculptures. Portraits of the emperors and their families were raised in a great and statues of the emperors and their families were number in the military camps and civil settlements along raised in a great number in the military camps and civ- the Limes. Numerous fragments of these statues are il settlements along the Limes in , in still preserved, but they have never been systematically and in . Though also in ritual registered. The paper introduces the project and the first contexts, there must have been bronze statues in con- results. Three different techniques of gilding have been siderable numbers. Many of these statues are likely revealed: besides leaf and fire-gilding, the unusual tech- destroyed by invading German troops in the middle of nique of diffusion gilding has been observed. Also vari- the 3rd century AD when the Limes was abandoned or ous repair techniques, different to those already docu- in case of Damnatio memoriae when the emporer fall mented for Mediterranean statues have been exposed. out of favor. (Fig. 1).

Fig. 1: Fragments of bronze statues from . Archäologisches Landesmuseum Baden-Württemberg. Scale 33 x 353 cm

239 Frank Willer, Roland Schwab & Kati Bott

Even if the fragments are often difficult to characterize and to categorize, they do constitute an important source for the reconstruction of imperial representation in the Limes forts and thus the importance of the imperial im- age in the .

Therefore, it is astonishing that they have never been compiled systematically. More than 4300 fragments from 124 different sites have been identified so far. Most of them have been archived for undefined old finds in mu- seums and other collections. Only a few significant frag- ments have been published in the serial “Der Oberger- manisch-Rätische Limes des Römerreiches” of the Reichslimeskommission since the end of the 19th cen- tury (see Sarwey et al. 1892). They were briefly reviewed in the works of Gustav Gamer (1969) and Oliver Stoll (1992).

Only a few better preserved pieces like a horse head from (Bakker 1985; Bergemann 1990), the portrait of Gordian III from Niederbieber (Fig. 2) (Lahus- en & Formigli 2001), or the so-called “Trajan” from the near (Schalles 2010) have already been presented in individual articles. Comprehensive publica- tions are available of scrap fragments from Colonia Au- gusta Raurica in (Janietz Schwarz & Rouill- er 1996; Janietz 2000) or recently of the well preserved statue of so called “youth from Xanten” (Schalles & Peltz 2012).

The project: aims, strategies and methods Fig. 2: Picture of the life-sized head of Gordian III from Nieder- bieber. Landschaftsverband Rheinland-LandesMuseum Bonn. The research project “Roman bronze Statues from the UNESCO World Heritage Limes” (2010-2014) is funded by the German VolkswagenStiftung and is initiated by the Archäologisches Landesmuseum Baden-Wuerttem- the public comprises an archaeological-historical ap- berg, the Institut für Archäologische Wissenschaften proach as well as the technological aspects. Casting of the Goethe Universität in a. M. and the techniques, alloy compositions and surface working like LVR-LandesMuseum Bonn (see Wessler 2011). Within gilding, chiselling, repair and joining are investigated by the initiative „Research in Museums“, the project is fur- different scientific methods. thermore supported by numerous partners of museums, universities and specialized research institutes in Ger- A lot of the technological details like casting flaws, re- many, and Switzerland. pairs, joints and the positions of chaplets can be revealed by carful optical surface observations and conventional Scientific investigations are performed by the Bunde- radiography. Computed tomography (CT) provides 3-D sanstalt für Materialforschung und -prüfung in Berlin, the information (Fig. 3) of more complex casting techniques Institut für Gießerei of the RWTH Aachen, the Instituut and makes it possible to investigate the interior surface. Collectie Nederland in Amsterdam, the Institut für Che- Based on the 3-D models casting simulations will be mie, Biochemie und anorganische Chemie of the Freie performed to visualize the entire process of casting, in- Universität in Berlin and the Curt-Engelhorn-Zentrum cluding solidification and shrinkage formation. For the Archäometrie in Mannheim. determination of the chemical compositions by ener- gy-dispersive x-ray fluorescence analysis (EDXRF), 370 The aim is to reappraise these important relicts of ancient samples were taken until now. Initial investigations of bronze casting to make them open for research and to the microstructure, corrosion, gilding and other surface

240 Large Roman Bronze statues from the UNESCO World Heritage Limes

that the prevalent alloy in Roman times is brass, one would expect most of the statues being of gunmetal. Actually the large statues are all of bronze (see also Caley 1970, Scott & Podany 1990; Oddy et al. 1990; Janietz Schwarz & Rouiller 1996; Janietz 2000; Lahus- en & Formigli 2001). Therefore we can follow Caley’s (1970) supposition, that most scrap used for casting statues is foundry waste or scrap coming from statues in turn.

Figure 4 shows the alloying components of samples analyzed so far and it attests the published data that Roman large statues are mostly made of leaded or even of highly leaded bronze. Consequently the well known leaf gilding (Fig. 5 a, b) is the predominately observed gilding technology of the statues (see Oddy et al. 1990; Oddy 2000). Only one fragment of an arm shows a pre- vious fire-gilded layer which was regilded by gold leafs (Fig. 6 a, b).

A very unusual and hardly observed technique of diffu- Fig. 3: Computed tomography of the head of Gordian III as shown sion bonding has been revealed at a back fragment from in figure 2 with a view inside. III Bundesanstalt für Material- a life size statute of a naked male deriving from an Ale- forschung und -prüfung, Berlin (BAM) mannic scrap depot of the early 4th century from Gross-Gerau in Hessen (Wenzel 2003; 2009), which were recently conserved in the LVR-LandesMuseum decorations are performed by metallography with optical (OM) and scanning electron microscopy (SEM) with at- tached energy dispersive spectroscopy equipment (EDX).

Apart from the categorization of the bronze fragments themselves, the reconstructions of the original statues, their locations and functions as well as aspects of pro- duction techniques will become more interpretable. The results are documented and recorded in an internet da- tabase, which is available to all participants during the whole project and which will also be available for every- body at the end of the project. a)

In addition to the research on bronze fragments, the compilation and analysis of all known statue bases with inscriptions is in progress. They are, as far as they are no bases for stone statues, directly and functionally as- sociated with the bronze statues. They can provide im- portant information on the source for the assembly and disassembly, and they are essential for the historical context.

Alloy compositions, surface decorations, experiments and exceptional casting techniques b)

Fig. 4: Histograms showing the lead (a) and tin concentrations According to a recipe given by Pliny, it is thought, that (b) of statues analyzed so far. Landschaftsverband Rhein- a third part of the bronze used for statues was scrap land-LandesMuseum Bonn and Curt-Engelhorn-Zentrum Archäo- (Caley 1970; Gazda & Hanfmann 1970). Bearing in mind, metrie, Mannheim

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Fig. 5a: Fragment of a garment (17 x 13 cm) from Groß-Gerau, Fig. 7a: Fragment of a gilded human back (60 x 42 cm) from with repair which has been done direct after casting. Groß-Gerau. 7b) Scanning electron image (backscattered mode) 5b) Leaf gilding with adhering lead corrosion. Landschaftsverband shows phase formation on the gold-base metal interface. Land- Rheinland-LandesMuseum Bonn and Curt-Engelhorn-Zentrum schaftsverband Rheinland-LandesMuseum Bonn and Curt-Engel- Archäometrie, Mannheim horn-Zentrum Archäometrie, Mannheim

Fig. 6a: Fragment of a gilded live-sized bronze arm (23 x 12 cm) of a statue from Bonn. 6b) Scanning electron image (backscat- tered mode) shows porous fire gilding with two outer layers Fig. 8: The X-ray dot map from the interface of the gilded back of gold leaf from regilding. Landschaftsverband Rheinland- from Groß-Gerau (see figure 7) illustrates the interdiffusion of LandesMuseum Bonn and Curt-Engelhorn-Zentrum Archäo- gold from the gold leaf and copper of the bronze. Curt-Engel- metrie, Mannheim horn-Zentrum-Archäometrie, Mannheim

(Fig. 7a , b). The surface beneath the gilding is heavily been done only to lead free bronzes, but several exper- corroded, but figure 8 clearly shows that interdiffusion iments showed that there is already a good adhesion of of gold and bronze has taken place. It is not clear if this the gold coating on leaded bronze after polishing a leaf technique is an accidental or an intentional one, but it onto the surface. The attachment can be improved by left uncompleted because of the interaction of the gold gentle heating the bronze, which is probably due to fast leaf with the lead of the alloy (Fig. 9). The eutectic point diffusion behavior of gold in lead forming the eutectic of Pb-AuPb3 is more than 100 °C lower than the melting with lead globules near the surface (Fig 11). point of lead (Okamoto 1993). Experimental reconstruc- tions (Bott 2011) of the diffusion gilding technology with On a bronze fragment from Groß-Gerau, a large surface highly leaded bronze revealed, that the eutectic is eas- repair technology with patches and copper rivets has ily formed and therefore the golden colour of the leaf been observed. This technology had previously been suddenly changes into gray (Fig. 10)1. One would expect considered to be a later repair of the damaged statue that a deliberate diffusion gilding of statues should have (see Fig. 4a). The findings from Gross-Gerau now

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Fig. 9: Lifting of a gold leaf by corroded lead on the surface of Fig. 11: Some experiment like in figure 9 after soft heating. The the back from Groß-Gerau (see figure 7. Scanning electron image gold leaf leaves unaffected, but the bonding is only mechanical- (backscattered mode). Curt-Engelhorn-Zentrum-Archäometrie, ly and can easily detached. Landschaftsverband Rhein- Mannheim land-LandesMuseum Bonn

Fig. 10: Experimental diffusion gilding with a high leaded bronze Fig. 12: Rectangular hole on the surface of a fragment of a life- alloy. After heating around 200 °C the Pb-AuPb3 eutectic appears sized bronze statue. These holes are typical relicts from chaplets. and the color of the gold leaf turns to grey. Landschaftsverband Landschaftsverband Rheinland-LandesMuseum Bonn Rheinland-LandesMuseum Bonn demonstrate, that this repair was immediately executed chaplets of statues coming from the Mediterranean area after the failed casting. It has been identified at several (Lechtman & Steinberg 1970; Willer 1994; Lahusen & other statue fragments from the limes region so that we Formigli 2001; Schalles & Peltz 2011). can assume this technique for repair was probably pri- marily used for difficult moulded large sized statuary. It Regarding the finds discussed here, the holes are small- is well known, that flawless complex castings were hard- er and usually plugged by small, wrapped bronze beads ly to produce with ancient technology and antique found- or even left open (Fig. 12). ry men usually decided to apply very time consuming repairs rather than melting down their spoiled castings A very particular phenomenon has been observed on (Lechtman & Steinberg 1970). Probably it was much the outer surface of objects from , Bonn and Co- more effort to produce a new mould and recast the hole logne. A uniform hexagonal network with each hexagon statue, than repairing the defects. being 1mm in diameter resembling honeycombs can be seen under the microscope (Fig.13). The statues coming from the Limes differ significantly to manufacturing techniques known from Mediterranean An identical pattern is published by Scott & Podany sculpture. Rectangular patches are well documented for (1990), observed on a bronze statue of Roma dated to repairs of casting flaws and holes from the removed 40-68 A.D. from the J. Paul Getty Museum in Malibu

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individual find spots. Technological features like repairs and founding do probably allow a more differentiated view and some specific techniques could be observed in certain regions so far. Discussing a chronological de- velopment is not possible at the moment, but the work is in progress. The quantitative estimation and chrono- logical classification of the different gilding techniques employed for example is restricted in terms of the small number of gilded fragments investigated so far, but leaf gilding seems to be the most popular one.

The destruction of the bronze statues and their post-Ro- man use as scrap metal is also important. Date and type of destruction can be examined at the fragments as well as the handling of scrap by Germanic looters or Roman Fig. 13: Patches of curious protruding round hemispheres en- scrap collectors for example. Marks of hammers, levers closed by a hexagonal network found on several bronze statues or chisels as well as scratches on the surface of gilded fragments. The picture shows a detail of the pattern on a fragment bronze are evidence of the demolition of sculptures by that was found in Cologne. Landschaftsverband Rheinland-Lan- desMuseum Bonn probably post-antique looters greedy for metal. Numer- ous small-scale fragments indicate the preparation for remelting (see e.g. Fig. 1).

(Inv. Nr. 84.AB.671). Scott & Podany (1990) are discuss- By its interdisciplinary approach, the project first aims ing this network in the context of the microstructure and at continuation of the research on statuary representa- composition of the bronze, which contains 6.5 % tin and tion north of the Alps to a crucial extent. Second, it offers 1.8 % lead. They suggest a relation of the hexagons to the possibility to work out the similarities or differences a slow cooling of the cast bronze and the reheating in between the military-dominated provinces and the Italian the annealing process. or Mediterranean regions in Graeco-Roman tradition.

The fragments from the Limes with those networks on At the conclusion of the research project, an internation- the surfaces are not yet analyzed, so it is too early to al symposium is planned. Following, the original finds state any interrelationship. There is quite different pos- and the research results will be presented 2014 in a sibly how this network could have been produced and joint exhibition of the LVR-LandesMuseum Bonn, the alloy composition, solidification and heat treatment are Limesmuseum Aalen and the Museum Het Valkhof (NL) likely to affect this structure. Regular geometric corrosion to the public. Last but not least the project offers a great is rarely reported (Werner 1967) and would also be de- opportunity to emphasize the importance of finds that pendent on the microstructure. Since the hexagonal are stored in museums for the UNESCO World Heritage pattern is only be seen in areas where cold work hasn’t Limes – exemplary with the outstanding group of Roman been done and due to the fact that a metal object cast bronzes Statues. usually carries the structure of the mould. One idea is at the moment, if the moulds could have been construct- ed by slabs of honeycombs. We are currently looking for possibilities to check this hypothesis. Footnote

1 All experiments were carried out by Frank Willer and Kathi Bott at the conservation department of the Landschaftsver- Conclusion band Rheinland-LandesMuseum Bonn by using experimen- tal produced alloys without any deliberate modern additions. There is some discussion about similarities of particular The thickness of the used gold leafs were similar to original roman material (less than 3µm). The work has been part of a statues and therefore about specialized workshops cast- diploma thesis (Bott 2011). ing large bronze statues (e.g., Janietz 2000; Schalles & Pelz 2011). It is most unlikely that heavy bronze castings have been transported several hundred of kilometers, but itinerant founders like early modern bell founders Bibliography could have left their marks within certain regions. The chemical compositions of Roman large statues from the BAKKER, L.: Limes give a quite uniform impression concerning the 1985 Reste monumentaler Kaiserstatuen und der Pferdekopf aus der Wertach. In: Die Römer in Schwaben. Arbeit- alloy compositions and impurity pattern. There are mar- shefte des Bayerischen Landesamtes für Denkmalp- ginal differences within the compositions between the flege 27, München, 104-105.

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BERGEMANN, J.: SARWEY, O., F. HETTNER, & FABRICIUS, E.: 1990 Römische Reiterstatuen. Ehrendenkmäler im öffentli- 1892 Der Obergermanisch-Rätische Limes des Römerrei- chen Bereich. Beiträge zur Erschließung hellenis- ches 1. Im Auftrage der Reichslimeskommission, Hei- tischer und kaiserzeitlicher Skulptur und Architektur 11, delberg. Mainz. SCHALLES, H.-J.: BOTT, K.: 2010 Kaiserbild oder Privatporträt? - Das römische Bronze- 2011 Vergoldungstechniken an römischen Großbronzen des bildnis in . Kölner Jahrbücher 43, 663-673. UNESCO-Weltkulturerbe Limes. Untersuchungen zur Diffusionsvergoldung an Bronzestatuen. Unpublished SCHALLES, H.-J. & PELZ, U.: diploma thesis, . 2011 Der Xantener Knabe. Technologie, Ikonographie, Funk- tion und Datierung. Xantener Berichte 22, Darmstadt/ CALEY, E.R.: Mainz. 1970 Chemical composition of Greek and Roman statuary bronzes. In: S. Doeringer, D.G. Mitten & A. Steinberg SCOTT, D.A. & PODANY, J.: (eds.), Art and technology. A symposium on classical 1990 Ancient Copper Alloys: Some Metallurgical and Tech- bronze, Cambride, 37-49. nological Studies of Greek and Roman Bronzes. In: M. True & J. Podany (eds.) Small Bronzes Sculpture from GAMER, G.: the Ancient World, Malibu, 31-60. 1969 Kaiserliche Bronzestatuen aus den Kastellen und Le- gionslagern an Rhein- und Donaugrenze des römis- STOLL, O.: chen Imperiums, Gießen. 1992 Die Skulpturenausstattung römischer Militäranlagen an Rhein und Donau: der obergermanisch-rätische Limes. GAZDA, E.K. & HANFMANN, G.M.A.: Pharos 1, St. Katharinen. 1970 Ancient bronzes: decline, survival, revival. In: S. Doeringer, D.G. Mitten & A. Steinberg (eds.), Art and LAHUSEN, G. & FORMIGLI, E.: technology. A symposium on classical bronze, Cambri- 2001 Römische Bildnisse aus Bronze. Kunst und Technik. de, 245-270. München.

JANIETZ SCHWARZ, B. & ROUILLER, D.: WENZEL, C.: 1996 Ein Depot zerschlagener Grossbronzen aus Augusta 2003 Verschrottete Kaiser. Ein Altmetalldepot des 4. Jahr- Raurica. Die Rekonstruktion der beiden Pferdestatuen hunderts n. Chr. aus Groß-Gerau. In: Hessen-Archäo- und Untersuchungen zur Herstellungstechnik. For- logie 2.2002, Stuttgart, 127-130 schungen in Augst 20, Augst. 2009 Der römische von Groß-Gerau, „Auf Esch“: die Baubefunde des Kastellvicus und der Siedlung des JANIETZ, B.: 2.-3. Jahrhunderts. Frankfurter Archäologische Schrif- 2000 Ein Depot zerschlagener Grossbronzen aus Augusta ten 9, Bonn. Raurica. Die Rekonstruktion der Gewandfiguren. For- schungen in Augst 30, Augst. WERNER, O.: 1967 Beitrag zur Phänomenologie der Korrosion und Patina- LECHTMAN, H. & STEINBERG, A.: bildung antiker Kupferlegierungen. Praktische Metallo- 1970 Bronze joining: a study in ancient technology. In: S. graphie 4(1), 3-15. Doeringer, D.G. Mitten & A. Steinberg (eds.), Art and technology. A symposium on classical bronze, Cambri- WESSLER, A.: de, 5-35. 2011 Interdisziplinäre Forschung an Museen – Wissen- schaftsförderung der VolkswagenStiftung. Museums- ODDY, W.A.: kunde 76, 1, /2011, pp. 32-37. 2000 A history of gilding with particular reference to statua- ry. In: T. Drayman-Weisser (ed.), Gilded metals: histo- WILLER, F.: ry, technology and conservation, London, 1-19. 1994 Zur Herstellungstechnik der Herme. In: G. Hellenkem- per Salies, H.-H. von Prittwitz und Gaffron & G. Bauch- ODDY, W.A., COWELL, M.R., CRADDOCK, P.T. & HOOK, D.R.: henß (eds.), Das Wrack. Der antike Schiffsfund von 1990 The gilding of bronze sculpture in the classical world. Mahdia, Kataloge des Rheinischen Landesmuseums In: M. True & J. Podany (eds.), Small Bronzes Sculp- Bonn 1, 2, Köln, pp. 953-970. ture from the Ancient World, Malibu, 103-124. OKAMOTO, H.: 1993 Au-Pb (Gold-Lead). Journal of Phase Equilibria 5(3), 648-649.

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