Excavations by MoLAS at 30 Gresham Street and 12 Arthur Street in the City of London in 2001 have led to a complete reassessment of the provision of Roman London’s water supply. Four massive first- and second-century wells contained remains of two types of mechanical water-lifting machines or bucket-chain systems. The discoveries allowed identification of a similar bucket-chain from the Cheapside Roman baths, found 50 years earlier by Ivor Noël Hume of the Guildhall Museum. Archaeological and engineering analysis has revealed the water-lifting capacity of the machines, which could have supplied a significant proportion of the town’s population with clean water.