In 1136, Baldwin de Redvers seized the castle as part of his rebellion against King Stephen. Although Stephen's army moved quickly to besiege the castle, Redvers was able to resist for three months until the failure of his water supply, which had been provided by a well and probably a rainwater cistern. It is possible that the absence of an eastern tower to match Athelstan's Tower is due to its destruction by undermining during this siege, and the discovery in c. 1930 of a short section of crudely-built tunnel leading towards this point of the wall has been interpreted as associated with this event. It is also likely that the barbican was captured and destroyed at this time.