A programme of excavations on and around the keep of Pevensey Castle established that the fort wall of the late Roman "Saxon Shore" fort was constructed AD 280-300, very possibly during the usurpation of Allectus. A deep sequence of "dark earth" built up against the inside of the Roman fort wall during the Roman and early medieval periods, before and after the establishment of William I's castle after 1066. A substantial stone keep and probably the gatehouse and inner bailey were constructed around 1200 and traces of a tower on the outside of the Roman fort wall were recorded. Substantial later repairs to the inside included the addition of a tower against the outer face of the (collapsing) Roman wall, the construction of a garderobe chamber and the re-building of the north-east tower, probably in the early 14th century. The base of the now ruinous keep was filled with clay after the 16th-17th centuries, probably to provide a foundation for cannon to defend the castle against possible Armada invasion in 1588.