Civil war broke out in England and raged between 1139 and 1153, forming a turbulent period in which the rival factions of King Stephen and the Empress Matilda struggled for power. Open battles were relatively rare during the war, with campaigns instead centred on a sequence of raids and sieges as commanders attempted to gain control over the vital castles that controlled the territory in the rival regions. Siege technology during the Anarchy centred on basic stone-throwing machines such as ballistae and mangonels, supported by siege towers and mining, combined with blockade and, occasionally, direct assault. The phase of the conflict known as "the Castle War" saw both sides attempting to defeat each other through sieges, such as Stephen's attempts to take Wallingford, the most easterly fortress in Matilda's push towards London, or Geoffrey de Mandeville's attempts to seize East Anglia by taking Cambridge Castle.