Montfichet's Tower was a Norman fortress on Ludgate Hill in London, between where St Paul's Cathedral and City Thameslink railway station now stand. First documented in the 1130s, it was probably built in the late 11th century. The defences were strengthened during the revolt of 1173–1174 against Henry II. It was demolished in 1213 by King John and the site sold in 1275 to build the great Dominican priory of Blackfriars. Archaeological excavations in 1986–90 uncovered waste pits and the remains of ditches between Carter Lane and Ludgate Hill.
Today The River Fleet has been reduced to a trickle in a culvert under New Bridge Street that emerges under Blackfriars Bridge, but before the development of London it was the biggest river in the area, after the Thames. It formed the western boundary of the Roman City of London and the strategic importance of the junction of the Fleet and the Thames means that the area was probably fortified from early times.