Pembroke began as an earthwork enclosed by Roger of Montgomery on a rocky riverside promontory in the 1090s. Later stone construction included William Marshal's massive cylindrical keep. The four-storey tower rose almost 24.5 metres, with thick walls and a stone dome. The inner bailey used river cliffs on two sides and a substantial curtain wall with flanking towers on the third. The larger outer bailey had its own stone curtain, corner towers, and a strongly defended gatehouse. Part of the southern curtain was built to double thickness for additional protection.
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Pembroke's river cliffs, cylindrical keep, and defended baileys
Pembroke combined natural river defences with a domed cylindrical keep, separate baileys, and extra masonry at vulnerable approaches.