Stephen responded by promptly moving south, besieging Arundel and trapping Matilda inside the castle. Stephen then agreed to a truce proposed by his brother, Henry of Blois; the full details of the agreement are not known, but the results were that Matilda and her household of knights were released from the siege and escorted to the south-west of England, where they were reunited with Robert of Gloucester. The reasons for Matilda's release remain unclear. Stephen may have thought it was in his own best interests to release the Empress and concentrate instead on attacking Robert, seeing Robert, rather than Matilda, as his main opponent at this point in the conflict. Arundel Castle was also considered almost impregnable, and Stephen may have been worried that he risked tying down his army in the south whilst Robert roamed freely in the west. Another theory is that Stephen released Matilda out of a sense of chivalry; Stephen had a generous, courteous personality and women were not normally expected to be targeted in Anglo-Norman warfare.