History of Bristol Welsh estate and Robert of Caen became the first Earl of Gloucester, c. 1122. He is believed to have been responsible for completing Bristol castle. In 1135 Henry I died and the Earl of Gloucester rallied to the support of his sister Matilda against Stephen of Blois who had seized the throne on Henry's death. Stephen attempted to lay siege to Robert at Bristol in 1138 but gave up the attempt as the castle appeared impregnable. When Stephen was captured in 1141 he was imprisoned in the castle, but when Robert was captured by Stephen's forces, Matilda was forced to
Henry I of England now had the best claim to the throne. William of Breteuil championed the rights of Robert, who was still abroad, returning from the Crusade, and to whom Henry and the barons had given homage in previous years. Henry argued that, unlike Robert, he had been born to a reigning king and queen, thereby giving him a claim under the right of porphyrogeniture. Tempers flared, but Henry, supported by Henry de Beaumont and Robert of Meulan, held sway and persuaded the barons to follow him. He occupied Winchester Castle and seized the royal treasury. Henry was hastily crowned king in Westminster