Roman water wheel
5 December 2002
Solving a 2,00 year old puzzle: The reconstruction of the Roman water-lifting machinery.
The engineers, archaeologists and timber construction specialists who collaborated earlier this year to recreate a 2,000 year-old water-lifting machine were faced with a complex problem. When the sophisticated Roman machinery was uncovered in Gresham Street in September 2001, key elements were missing and there were no written instructions.
Yet by comparing evidence from the surviving remains with known examples of ancient engineering - and supporting these theories with modern engineering principles – these experts were able to reconstruct a unique machine, which in its original form would have been capable of raising an astonishing 72,000 litres (15,000 gallons) per 10-hour day.
The project has taken 6 months on the drawing board, one month testing prototypes and 6 weeks under construction. The diary of its reconstruction will form a Channel 4 Time Team documentary to be shown next year.
The surviving ironwork and wood made it possible for engineers Tony Taylor of Foggo Associates and Dr Bob Spain to calculate the probable weight of the chain, buckets and water, but there were countless questions to answer:
- What would have been used to turn the bucket and chain?
- How would water have been collected from the buckets?
- How was the drive wheel powered, and how much water would it have lifted?
Construction experts, McCurdy & Co were appointed to build the machinery. They combined their knowledge of medieval and later woodworking with that of ancient timber specialist, Damian Goodburn, to construct something that was feasible for the Roman period and workable in the 21st century.
The result was a series of drawings of how they thought the water-lifting machine might have worked. A series of trials were then carried out to test the various engineering elements that made up the water-lifting machine. This was done in the McCurdy yard using plywood versions of the drive wheel and bucket chain.
A prototype of the drive wheel and gearing mechanism was tested and modified, along with variously shaped compartments used to retain the water, to achieve an optimum discharge.
In order to observe the interaction of iron elements of the chain with the wooden buckets, ply-wood mock-ups of all the elements were linked together to form a continuous chain. These were suspended over a prototype drive-wheel to see how the chain would rotate. Once testing was complete, McCurdys went into production of the component parts.
The completed machinery consists of an 8-sided oak drive wheel with water buckets that empty into a trough as they near the top of the chain. The 18 oak buckets are made from planks with a recessed base to allow room for the articulated movement of the iron chain.
As Roman wrought iron has a higher carbon and silicon content than modern wrought iron - making it less prone to corrosion - specialist firm Chris Topp & Co were invited to recreate the chain from puddled iron, the nearest modern equivalent.
The final full-scale reconstruction, on view outside the Museum of London, has been made with a capstan and gears, and will be operated by a trained demonstrator assisted by members of the general public. It will be on display from 5 December 2002 until the end of May 2003.
Editor's notes:
The Gresham Street site was excavated in 2001 by the Museum of London Archaeology Service in collaboration with AOC Archaeology Group.
- Service in collaboration with AOC Archaeology Group.
- Archaeological specialists: Ian Blair and Damian Goodburn
- Project Engineers: Tony Taylor of Foggo Associates together with Dr Bob Spain
- Construction: McCurdy & Co Ltd, Stanford Dingley, Reading RG7 6LS
- Ironwork: Chris Topp & Co, Carlton Husthwaite, Thirsk YO7 2BJ
- Sponsor: A Sharing Solutions initiative by Swiss Re – towards a sustainable future.
Swiss Re is one of the world’s leading reinsurers. As a centre of competence in risk management, it fosters an open, constructive water dialogue to develop best water management practices.
Swiss Re’s Sharing Solutions initiative not only provides funds but also contributes expertise and knowledge-exchange in finding sustainable solutions.
Further information:
Judith Holmes: 020 7814 5502
Fay Ross-Magenty: 020 7814 5503