At first, the balance of power appeared to move slightly in Matilda's favour. Robert of Gloucester besieged Stephen in 1143 at Wilton Castle, an assembly point for royal forces in Herefordshire. Stephen attempted to break out and escape, resulting in the Battle of Wilton. Once again, the Angevin cavalry proved too strong, and for a moment it appeared that Stephen might be captured for a second time, before finally managing to escape. Later in the year Geoffrey de Mandeville, the Earl of Essex, rose up in rebellion against Stephen in East Anglia. Geoffrey based himself from the Isle of Ely and began a military campaign against Cambridge, with the intention of progressing south towards London. Ranulf of Chester revolted once again in the summer of 1144.