The north tower is an apsidal, or "D-shaped", design that is characteristic of Welsh castles of the early 13th century. Originally it may have contained either a hall or a chapel. What is today the middle tower was originally the southernmost part of the defences, but now leads through the Edwardian ditch yard to the south tower, another apsidal design that once contained spacious accommodation. Both the apsidal towers lacked fireplaces in the main chambers, instead using central heaths to heat the rooms.