Buckets and chain
In 2001, archaeologists working on a large-scale excavation at 30 Gresham Street, in the City of London, made some intriguing discoveries. At the foot of a deep well dug in 108-109 AD (it was dated by dendrochronology, or tree-ring dating of timbers used in its construction), they found sections of a massive iron chain and a series of oak 'buckets' or containers, each capable of holding up to seven litres of water.

Perfectly preserved in the waterlogged conditions at the bottom of the well, some of the finds were in such good condition that it was thought they must have fallen into the well recently. The iron, in particular, seemed in such good condition that the archaeologists wondered at one stage whether it might be part of some modern-day machinery that had been dumped or fallen into the well.

Water-lifting machine
In fact, what they had found were the remains of a Roman water-lifting machine. When it was working, this would have consisted of a chain of 30 oak buckets, joined by large wrought iron links and capable of raising up to 7,200 litres (1,500 gallons) of water per hour. The remains appear to have fallen into the well when a fire (possibly the 'Hadrianic' fire, which devastated Roman London in 125 AD) destroyed the machine and a building above it. There they remained undisturbed until a major redevelopment scheme in the City of London led to their excavation almost 1,900 years later.

Time Team filmed the Gresham Street excavation for the documentary Londinium: Edge of Empire, first screened in 2002. After the excavation, the Team also followed the efforts of archaeologists and other specialists as they tried to make sense of the finds, to put them back together – and then to construct a Roman-style water-lifting machine, making use of the evidence provided by the Gresham Street dig.

Reconstruction challenge
The Museum of London, whose archaeologists conducted the Gresham Street excavations, brought together a team of experts to rise to the water-lifting challenge. Working with the Reading-base engineering firm, McCurdy & Co, their objective was to construct a working machine that used the same 'chain and bucket' system as found at Gresham Street and could have been built by the Romans with the tools and knowledge available to them at the time.

Even after the initial mystery of the Gresham Street finds was solved and they were identified as part of a Roman water-lifting machine, it still required a lot of detective work to figure out how the bigger structure would have worked. First, the experts calculated the basic dimensions of the machine.

By measuring the depth of the well and the sizes of the oak buckets and iron links, they worked out that there must have been 30 buckets in the chain. When filled with water, each bucket would have weighed 14kg. In addition, the metal components for each bucket weigh approximately 6kg. So the total weight of the bucket chain could have been at least 500kg, or half a ton. Clearly, the structure necessary to support and drive such a heavy weight would have been no mean engineering feat.

Other clues
The reconstruction team was able to get other clues about the design of the original machine from the components found at Gresham Street. For example, the shape of the iron links indicated that the original drive wheel must have been facetted, or had flat sides. Extensive testing on a plywood model – initially built with seven sides – showed that an eight-sided version was most efficient at raising water.

Other evidence for how the Romans went about constructing such machines came from excavations in Italy. A bucket-chain used to supply the public baths in Cosa, for example, is very similar to the one found in Gresham Street; while at Pompeii, two bucket-chains have been excavated that used to provide water to the Stabian Baths from a deep well.

But no one could be sure exactly how the Roman machine would have looked or worked. With no fixed model on which to base their design, the reconstructors were engaged in an archaeological experiment – and opinions often differed, sometimes strongly, on how the Romans might have done things.

Brew of controversy
Time Team's Mick Aston stirred the brew of controversy with his insistence that the modern-day reconstruction was 'over-engineered'. He felt that the Romans would have adopted a much more 'rough and ready' approach, not relying on the detailed calculations underlying parts of the reconstruction design.

In the end, the reconstruction team was forced into just such an approach as saws, hammers and chisels were put to work on the assembled machine so that the timbers of the main drive wheel interlinked properly with the bucket chain. On the spot adjustments were continuing right up to the day when the machine was due to go on display at the Museum of London. Indeed, the machine was finally assembled at the museum in just two days as the team rushed to meet the deadline – an achievement that even the Roman engineers who built the Gresham Street machine might have struggled to match.

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