The earlier phase, likely completed before Hugh’s death in 1186, comprises the Trim gate on the western wall and a series of rectangular, open-backed towers along the river front. These structures represent the defensive priorities of the late twelfth century, with the river-front wall ingeniously incorporating the natural rock outcrop as part of its defences, requiring only a stone facing rather than a fully constructed wall. The second phase, probably dating to Walter’s work between 1201 and 1207, introduced more sophisticated D-shaped towers along the southern side and the impressive Dublin gate, reflecting evolving military engineering techniques of the early thirteenth century.

The defensive structures reveal fascinating details about medieval castle life and warfare. Tower 3, known as the Magdalen Tower, stands as a substantial square structure at the northern apex, originally featuring a basement with wooden floors and two upper levels fitted with long arrow loops accessed via mural passages. Its conversion to a solar, or private chamber, in the fourteenth century involved mining back the inner walls to create more living space, demonstrating how castles evolved from purely military installations to more comfortable residences. The southern curtain wall’s five D-shaped towers, designated A through F, each contained two to three levels with timber floors and arrow loops strategically positioned to cover adjacent sections of wall. Archaeological excavations by Sweetman in 1978 revealed that these towers were later filled with rubble and clay in the seventeenth century to create artillery platforms, with some grim discoveries including severed heads in tower C and burials at tower D’s base.

The Dublin gate represents the pinnacle of the castle’s defensive architecture, surviving almost perfectly intact as a subcircular structure rising three levels high. Its sophisticated defence system included dual gateways at either end of the entrance passage, two murder holes, and a portcullis, whilst a wooden bridge connected it to a forward barbican with its own gateway and defensive loops. The interior featured mural passages leading to four arrow loops, a garderobe, and a newel staircase connecting the levels, with later additions including a fireplace at first floor level and windows with seats overlooking the inner doorway. Throughout the castle, evidence of multiple building phases can be traced; from the original twelfth-century construction through fourteenth-century residential conversions to seventeenth-century military adaptations, creating a complex archaeological record that includes pottery finds dating from the thirteenth century onwards and structural modifications that tell the story of changing defensive needs and domestic arrangements over five centuries.