Before long, a polygonal shell keep was placed on the motte and a new wall was built on top of the bailey rampart. The rampart is so powerful that the curtain only needs to be of modest height.

During the Elizabethan modifications, artillery bastions were added at the south corners of the curtains, but encased within both are square, open-backed towers. Clearly, they are early examples of mural towers and they are too small and too widely spaced to be effective as flankers. They support the written evidence that the curtain was built by Baldwin de Redvers.