In the centre of the fortification was the keep, built up from the round tower of 1512–14, and of the original building's walls were incorporated into the new design. The original tower had ten gunports embedded at ground level in its walls, but these were blocked up in the second phase of building. The keep would originally had a parapet running around its roof, which was initially flat but converted to a ridged design in the third phase of work. The ground floor was laid in brick and had a brick and stone-lined well to supply it with water. The keep had two fireplaces, but these were small and not intended for cooking – indeed, the final version of the keep was probably never used as a living space. The first floor windows were added in the final phase of work; they were not intended for use as gunports, but they had bars and shutters, so could have been easily secured in the event of an attack.