Flint's donjon and independent sea supply

Flint's enlarged, isolated corner tower serves as its main stronghold, or donjon, an unusual arrangement among British castles. Its walls are described as seven metres thick at the base and five metres above, with entry requiring access to the first floor. A surviving arrow slit illustrates how attackers crossing the bridge towards the inner ward would face fire from behind as well as from openings in the great tower. Reaching the inner ward still left a further drawbridge to the donjon. The tower could receive supplies by sea, giving its defenders a means of holding out separately. This unusually strong arrangement was expensive and depended on Flint's geography, which limited its usefulness as a model for other sites.