Wisbech Castle was a stone to motte-and-bailey castle built to fortify Wisbech on the orders of William I in 1072, it probably replaced an earlier timber and turf complex. The layout was probably oval in shape and size, on the line still marked by the Circus. The original design and layout is unknown. It was rebuilt in stone in 1087. The castle was reputedly destroyed in a flood in 1236. In the 15th century, repairs were becoming too much for the ageing structure, and a new building was started in 1478 under John Morton, Bishop of Ely. His successor, John Alcock, extended and completed the re-building and died in the Castle in 1500. Subsequent bishops also spent considerable sums on this new palace. The Bishop's Palace was built of brick with dressings of Ketton Stone, but its exact location is unknown.