The stone-faced ditch is guarded by fifty-four gun ports set in the curtain, each one in a small chamber reached from the gallery at basement level. The gun ports are widely splayed embrasures typical of the Henrician era. One of the outer lobes is higher than the rest and contains the entrance, formerly reached by a drawbridge across the ditch.

Within the gate passage are all the traditional trappings of defense - portcullis groove, studded oak gates and murder holes in the vault. To reach the central tower, it is necessary to pass through the courtyard, in fact no more than a curving corridor between the central tower and the curtain. It would have been a death trap for attackers attempting to make their way to the tower entrance while under fire from either side.

The central tower had store rooms, garrison's lodgings and the governor's residence crammed into its three floors. Timber partitions radiate from a central stone shaft, which contains a spiral stair.