The Keep of Carisbrook Castle, Isle of Wight
The keep was the first part of this 13th century castle to be built. After the keep was completed, the castle’s thick curtain walls could be constructed around it. The keep was shaped like an irregular polygon and to make it easier to defend a single gate was built into it, with a portcullis for extra protection. Seventy-two steps, each nine inches in height were built leading up to the entrance making it very difficult for invaders to get to. It is thought that the keep was actually taller than it is today, and those defending the castle could attack invaders from this point with great success. There was a well within the keep which it is said was over three hundred feet deep.