The English Civil War broke out between the supporters of Charles I and Parliament in the 1640s; with the king and Parliament maintaining their capitals in Oxford and London respectively, the Thames Valley once again became a critical war zone. Wallingford was a Royalist town, with a garrison established there in 1642 to prevent an advance on Oxford to the north-west. Colonel Thomas Blagge was appointed governor, and in 1643 the king instructed him to refortify the castle, inspecting the results later that year. By 1644, the surrounding Thames towns of Abingdon and Reading had fallen and Parliamentary forces unsuccessfully attacked the town and castle of Wallingford in 1645. General Thomas Fairfax placed Wallingford Castle under siege the next year; after 16 weeks, during which Oxford fell to Parliamentary forces, the castle finally surrendered in July 1646 under generous terms for the defenders.