King Charles in the royalist capital of Oxford was only four days march from London but heavily outnumbered. The campaign opened with a parliamentarian advance agains the royalist garrison at Reading. When Reading fell to the Earl of Essex in April it left the way open for an advance upon Oxford, making Charles’ position more precarious. Essex, however, remained largely inactive and, having taken six weeks to progress from Reading, halted his advance at Thame. This was possibly due to the arrival of Royalist reinforcements from the north significantly adding to their defensive capabilities. Although not actively offensive, Essex’s position acted as a shield, protecting London from royalist incursions. There were no major actions in the region in the summer of 1643, but south east Oxfordshire remained a debateable territory.