The war continued indecisively over the next couple of years, and Henrietta Maria returned to Britain for 17 months from February 1643. After Rupert captured Bristol in July 1643, Charles visited the port city and laid siege to Gloucester, further up the river Severn. His plan to undermine the city walls failed due to heavy rain, and on the approach of a parliamentary relief force, Charles lifted the siege and withdrew to Sudeley Castle. The parliamentary army turned back towards London, and Charles set off in pursuit. The two armies met at Newbury, Berkshire, on 20 September. Just as at Edgehill, the battle stalemated at nightfall, and the armies disengaged. In January 1644, Charles summoned a Parliament at Oxford, which was attended by about 40 peers and 118 members of the Commons; all told, the Oxford Parliament, which sat until March 1645, was supported by the majority of peers and about a third of the Commons. Charles became disillusioned by the assembly's ineffectiveness, calling it a "mongrel" in private letters to his wife.