An astonishing find by Museum of London archaeologists, announced last year, suggests that medieval Londoners had access to a huge riverside wheel downriver at the nearby village of Greenwich.
Excavations at Greenwich Wharf have uncovered the foundations of London’s earliest found medieval tide-powered mill. The huge structure, measuring ten metres by twelve metres at its base, would have had a wheel diameter of over 5 metres and has been dated to the twelfth century. The mill structure represents an extraordinary example of medieval engineering ingenuity.
Tidal mills worked by drawing in water from the river as the tide rose and releasing it as it fell, powering the mill. The mill at Greenwich features a substantial fragment of intact waterwheel and an enormous trough to channel the water which was shaped out of a single oak beam.
Remarkably well preserved in riverside peat deposits, the mill is an unprecedented and rare find. It appears to have been constructed in two phases from prepared oak beams, on which carpenters’ construction marks are still clearly visible.
Damian Goodburn, Museum of London’s ancient timber specialist identified the beams as being cut with an axe rather than a saw, initially suggesting an early medieval date. Dendrochronological analysis (where tree rings are counted) has supported this observation dating the trees’ felling to 1194.
A large curved section of the waterwheel itself was found preserved within the water trough allowing archaeologists to estimate the diameter of the wheel at around 5.2 metres – an incredible size for a wooden structure of this type and testament to the craftsmanship and engineering skills of its makers.
The mill was found sealed within a thick peat deposit, which, due to its anaerobic environment, has meant that the timbers were extremely well preserved and fine construction details such as the carpenters’ (or millwrights’) assembly marks are still clearly visible on the timbers. These marks help to show how the building was prepared and assembled immediately prior to its construction and can also help to shown how the building may have been dismantled or demolished.
Despite the discovery of the waterwheel, confirming its use as a mill, no evidence for the gearwheels or the mill pond, which would have collected river water as the tide rose, were found. Numerous fragments of broken millstone were however discarded within the structure and were possibly reused, once worn-out, as packing material beneath the mill foundation.
The tidal mill was discovered during archaeological investigations by Museum of London Archaeology, working closely with Erith Contractors Ltd to prepare for the construction of a new residential development by London and Regional Properties at Greenwich Wharf in Greenwich.
Simon Davis, Contract Manager for Museum of London Archaeology, said: "Tide mills may have been numerous along the Thames foreshore in the early medieval period. Four mills in Greenwich are mentioned in the Domesday book of 1086 and over 6000 mills were recorded across the country at this time. However, little evidence of mills in use in the early medieval period has been found on archaeological sites, so the discovery of a 12th century tide mill at Greenwich is very significant and exciting. Detailed recording of the find following its excavation and dismantling by the Museum of London Archaeology field team will enhance our understanding of milling technologies and early medieval economies."
Mark Stevenson of English Heritage said, "The discovery of the remains of this wooden tidal mill at Greenwich Wharf, Greenwich, is likely to be the earliest medieval example of this type to be excavated in London. English Heritage is working closely with Greenwich Borough Council, the developers and Museum of London Archaeology to ensure that this rare and important discovery is carefully recorded."
Following consultation with English Heritage, who continue to monitor the site, the structure has been dismantled, with each timber carefully recorded so the mill can be properly researched. Key sections of the find, including the trough and the waterwheel, have been removed and are currently undergoing conservation by the conservation department at York Archaeological Trust.