Roman Artillery

11 mins read

Around 100 AD, a major Roman technological advance took place in the manufacture of catapults. A new design was introduced which increased their penetrating power by at least 50%. Here we describe how both the old and new catapults worked. Every archaeologist, if they are lucky, makes one, once-in-a-lifetime discovery. I have just made such a discovery in Croatia, the most remarkable site that I have ever, and will ever, have the privilege of being involved in. The site is the valley of the river Cetina, where the level of preservation is quite exceptional and the finds are unexpectedly magnificent.
Throughout the 1990s, I, together with the Department of Archaeology at Birmingham University, was involved in a project to investigate the islands along the coast of the former Yugoslavia. However, in the late 1990s, the local museum archaeologist, Ante Milosovic, began collecting an enormous amount of metalwork from the valley of the River Cetina, 50 miles inland from Split (which many readers of CWA will know as the site of Diocletian’s Palace). Dozens of objects – swords and helmets, spears and daggers, stone axes and jewellery, dating from the Neolithic through to the Medieval period were literally picked from the river bank by archaeologists or even casual walkers. Unfortunately, civil war was raging, and thus few outside Dalmatia were aware of the scale of the discovery.
In 2001 Ante Milosovic invited me and Darja Grossman from Ljubljana University to look at the sites and finds from the river. Would we be interested in studying the archaeology of the valley? Even though I was well aware of the finds from the area generally, nothing prepared me for the actual scale and significance of the Cetina material. The finds begin in the Neolithic and Bronze Age. The valley around Sinj (c. 80 square kilometres) actually contained a string of preserved settlements dating from the early Neolithic through to the Iron Age. Some of these were up to 1.5 hectares in size, occupied complete islands in the middle of the river. And then there was the metalwork. More than 60 swords, together with 30 complete or fragmentary Greco-Illyrian helmets of the mid first millennium BC were recovered from the river near the settlements – but specifically at Trilj where there was a ford and a confluence with a smaller river. It was also clear that there were many more objects still unpublished within the local Museum and that the actual number of finds was more comparable to one of the great rivers in Europe – rather than a small river in Dalmatia!
The Cetina is one of the most beautiful rivers in Croatia. The river rises high in the the mountains that border Bosnia and passes at first through land which is virtually a limestone desert; it then emerges into a series of fertile valley basins before passing through the Dinaric Alps in a most impressive gorge before reaching the sea at Omiš. The central part of the river valley is particularly significant. Here the river also connects with the great pass at Klis where a narrow route passes through the Dinarics and connects with the Salonitan plain, the provincial Roman capital at Salona and, of course, modern Split and Diocletian’s Palace. The valley is essentially a crossroads with routes passing east into Bosnia and the heart of the Balkans, west to the Adriatic, north to Zagreb and central Europe and south to the Nerteva and southern Europe. The river has thus often functioned as a border. During the late Roman period the river clearly formed a boundary between the Roman populations on the coast and the emerging Slavic principates, whilst the pass at Klis was a point of conflict between the Venetian and Turkish empires for more than a century. Not surprisingly, the archaeology of the river valley reflects this peculiar situation. Aside from a string of fairy-tale castles perched high on mountains, the valley boasts one of only two legionary fortresses in the Roman province of Dalmatia. Tilurium (modern Trilj) lies high above the valley guarding the passes south and a strategic ford across the river at Trilj. Along with the Colonia at Aequum these historic sites are essentially the sum of knowledge for most archaeologists who possess a passing familiarity with the region.
And then there is the Cetina Culture. The Cetina Culture is something of a mystery. Broadly equivalent to the Beaker period, this prehistoric culture might be compared to the Wessex Culture in Britain – it is largely defined on the basis of grave goods and ceramics which include rather exotic beaker forms, wristguards, arrowheads and simple metal objects which would also bear comparison with Beaker assemblages elsewhere in Europe. The Cetina Culture also has a very widespread distribution, ranging from the head of the Adriatic down to the southern Balkans.
Nearly 50 years ago, archaeologists led by Ivan Marovic from the Archaeological Museum in Split carried out a series of excavations in advance of a new hydro-electric plant. For the most part these were directed at the tumuli associated with the Cetina Culture and essentially allowed archaeologists to define this group. However, one small excavation was also carried out near the river in the valley basin near Sinj at a site called Otok (Croatian = island). Marovic revealed the timber settings of a prehistoric settlement preserved as a consequence of waterlogging. These excavations were small and were only published in the last year: few people outside the region were aware of the discovery.
Locally however a surprising amount of metalwork, of all periods, was being found in the river. The then local museum archaeologist, Ante Milosevic (now Director of the National Museum of Croatian Archaeological Monuments in Split) collected information on these. In the early 1990s this situation changed: in 1992 the dam was damaged in the civil war, and the river channel was cleaned, and as a result of changes in water flow, an enormous amount of metalwork was discovered.
And then there was also the numerous timbers, projecting from the riverbed. There is a huge area of marshland, not unlike the Somerset levels, and covering some 80 square kilometres. Here there is a string of settlements dating from the early Neolithic through to the Iron Age. Some are up to 1.5 hectares in size, occupying complete islands in the middle of the river: they could easily be compared with the classic lake villages of Switzerland or the Ljubljansko Barje in Slovenia.
But are these really in their original position? Has the river really been stable for 4000 years? I immediately contacted David Smith, the environmentalist at Birmingham, and it was arranged that he and Dr Andy Howard, a geomorphologist from Newcastle, should travel to the Cetina to carry out an environmental assessment. They were amazed by what they found. It was clear that not only were there extensive, preserved settlement areas, but the river was stable, and given the extent of waterlogging, that a significant part of the central valley probably preserved the prehistoric landscape associated with the preserved settlements. We carried out coring, and the environmental columns stretched back at least 8,000 years in preserved peat and organic deposits up to 3 metres in depth. Given the lack of environmental data between the Swiss alps through to Northern Greece, it was clear that the Cetina could provide an environmental baseline for much of the region. It felt like standing on the edge of the Somerset levels 100 years ago, said the environmentalists. The preservation equals that of the Swiss lakes, while the finds were comparable to the Thames! Their only comment was ‘Where do you start?’
Why is the material so spectacular? Dalmatia is noted for its lack of mineral resources – although Bosnia does possess some. In any case why is this material still preserved? Here we can consider the full range of reasons frequently trotted out for comparable events elsewhere in Europe. Casual loss – perhaps associated with frequent passages across the Trilj ford? This might explain some of the material, – but it hardly explains the presence of nearly 30 Greco-Illyrian helmets. The consequence of battle? What little we know of prehistoric warfare would suggest that if there was a battle and these items belonged to the dead they would most likely have been looted as trophies. Weaponry and defensive armour of this sort was always prized. Are these objects coming from settlements? Possibly, but given the number of swords one has to imagine displays of arms similar to that seen in a Scottish baronial castle! It actually seems more reasonable to suggest that the majority of this material has been placed in the river deliberately, and we are led, perhaps unwillingly, to suggest that this was for ritual purposes. At this stage we cannot say what such a ritual might be, but the presence of such material in a river, in a region where water resources are scarce and unreliable, is unlikely to be a coincidence.
Unfortunately, the valley is under threat from changes to water levels and development. Any changes to the water regime are likely to damage the delicate ecosytem which is preserving the environmental remains. As it is, the river banks are eroding. In some places house timbers 30cm square and up to 2.5 metres in length protrude from the riverbanks. Artefacts are eroding from the banks and it is likely that some looting is taking place. What happens next? Following initial work by Birmingham and Croatian partners, the British and Slovenian Academies have supported a 3-year international programme to plan and seek funding for extensive work. An application has been made to NERC to provide some funding for environmental research, but this is just a beginning. With a bit of luck, we hope to make Cetina a major contribution to the archaeology and environment of Central Europe and the Balkans.

Early artillery
c. 400 BC – AD 100
Torsion artillery was apparently invented in a Greek workshop in Sicily early in the fourth century BC. Each machine was powered by two spring-bundles formed by ropes of twisted sinew or hair. At top and bottom of each spring-frame the rope was threaded under tension through a round metal washer and over a metal crosspiece, up and down until the washer was filled. Bow-arms embedded in the springs projected outwards, and a bow-string was stretched between their far ends. Since washer and cross-piece could be rotated in a metal counterplate fixed to the wooden frame, the spring-bundles could be twisted to tighten them and increase the stored torsion power. Between the springs ran the stock, which comprised a fixed part, the case, and a moving part, the slider. The latter, carrying at the back a claw and trigger mechanism, was slid forward to engage the bow-string, and a winch operated by hand-spikes and a ratchet and pawl mechanism then hauled it back, pulling the arms together and tightening the springs. When the bow-string was released, the energy stored in the springs was imparted to the missile, its velocity rising as it accelerated down the slider. Both arrow-shooters and stone-throwers were made, each in a variety of calibres, and experimental reconstructions have shown that missiles may have been hurled 300 or even 400m.

Dating the change
When did the change happen? In the civil wars of AD 69, the Year of Four Emperors, the Roman army was still using old-style catapults. The armour plating from the front of two such catapults was found on the site of the second battle of Cremona, and the late-first-century tombstone of the military engineer (architectus) Gaius Vedennius Moderatus clearly depicts this sort of machine. Contemporary writers use old-fashioned terms for artillery: scorpio for a light arrow-shooter, catapulta for a heavier arrow-shooter, and ballista for a stone-thrower. The engineer Frontinus, writing in the 80s or 90s AD, specifically stated that there had been no recent innovations in engines of war. We find the earliest evidence for the new machines on Trajan’s Column (erected AD 113) and in Heron’s Cheiroballistra (probably c. AD 100). Later writers transfer the term ballista from stone-thrower to arrow-shooter. A date around AD 100 seems highly likely.
And the inventor? We will never know for sure, but a good guess would be Apollodorus of Damascus. Rome’s chief engineer under Trajan (AD 98-117) and Hadrian (AD 117-138) until his banishment in AD 129, his building projects included military bridges over the Danube, Trajan’s Forum in Rome, Trajan’s Arch at Ancona, and Hadrian’s Temple of Venus and Rome. He also wrote On Engines of War, a treatise which survives – though it does not describe the new type of artillery.
Whether or not Apollodorus was the inventor, the evidence for a technological revolution in artillery design around AD 100 now seems compelling. The new machines, ballistae for arrow-shooting and onagri for stone-throwing (see box feature ‘Stone-throwers’), would remain in service for 500 years. Then, soon before AD 600, there was a second artillery revolution – and the last before the invention of cannon. Torsion artillery was replaced by the crossbow for shooting arrows and the trebuchet, powered by men pulling ropes or later by a heavy counter-weight, for hurling stones.

Early stone-throwers, though different in detail and heavier, worked on exactly the same principle as arrow-shooters, the bow-string carrying a flattish pouch at the centre to propel the stone. They were called ballistae to distinguish them from arrow-shooters (catapultae). But by the third if not the second century AD, the term for a stone-thrower had changed to onager or scorpio. The tail of a scorpion, explains the Christian writer Tertullian in the early third century, ‘rising in a curved sweep, draws its hooked point up on high like an engine … For this reason the military machine, which activates its missiles by retracting, is also named after the scorpion.’ Ammianus Marcellinus, the fourth-century historian, agrees: ‘A scorpio is so called because it has its sting upraised above it.’
There is no dispute that machines with a sling attached to the end of a single arm, throwing stones by swinging them upwards and over, were in use by the fourth century. But Michael Lewis is convinced they came in much earlier, when the terms used for artillery changed comprehensively about AD 100, and a new design for stone-throwers complemented that for arrow-shooters. Experiments show that the onager outperforms the earlier stone-thrower by roughly 80%. ‘The reason is simple,’ says Lewis. ‘The greater arm-swing allows a longer time for acceleration, and the much greater length of arm-cum-sling imparts a still greater velocity to the missile. Speed at discharge is the fundamental secret.’

A note on sinew rope
What do you use to make a quality spring for an ancient catapult? All ancient writers agree that it is animal sinew, and a Vindolanda tablet records delivery of 100lbs of ‘ballista sinew’.
Michael Lewis explains why it mattered so much: ‘The arc of the bow-swing was only one of two basic parameters determining the power of ancient artillery. The other was the elasticity of the actual spring itself, which is central to the rate of acceleration when you discharge. Before the revolution, either hair or animal sinew was used for springs. After it, the ancient texts refer only to sinew. Hair was no longer adequate. Only animal sinew was elastic enough. The problem is that no one has ever made enough sinew rope to build a full-size reconstruction based on this material.’
Among several attempts to make sinew rope, that of architect and archaeologist Digby Stevenson has been the most successful. Using sinew from cattle and American elk, he first cut away all excess meat and fat (to reduce the stench!), and then allowed the sinew to dry out naturally over about a week. The sinew was then pounded with a hammer and shredded with a metal comb to separate out the individual fibres – a laborious and time-consuming procedure for which there were no short-cuts. The fibres were then spun into yarn, a process that could be done by drop-spindle, spinning wheel, or manually by fixing one end in place and twisting in the fibres while keeping the yarn extended and taut. Next, the finished yarn was twisted into strands of rope (each of eight or nine threads’ thickness), and finally these strands were twisted together to form three-strand rope. This could now be wound onto a spring-frame under tension until a full spring-bundle comprising many thicknesses of rope had been formed.
Digby Stevenson’s experiments have shown that the production of sinew rope for ancient catapults was a skilled, time-consuming and expensive process. What we do not yet know is just how powerful a catapult using sinew rope would have been. To find out, someone will have to make a lot of it. At least we now know how.

Source: Digby Stevenson, [email protected]

This article is an extract from the full article published in World Archaeology Issue 3. Click here to subscribe

Leave a Reply

Your email address will not be published.