By 1303, the English again held the upper hand, and Stirling was the last remaining castle in Scottish hands. Edward's army arrived in April 1304, with at least 17 siege engines. The Scots, under William Oliphant, surrendered on 20 July, but part of the garrison were ordered back into the castle by Edward, as he had not yet deployed his latest engine, "Warwolf". Warwolf is believed to have been a large trebuchet, which destroyed the castle's gatehouse. Although Edward's victory seemed complete, he was dead by 1307, and Robert Bruce was now King of Scots. By 1313, only Stirling, Roxburgh, Edinburgh and Berwick castles were held by the English. Edward Bruce, the king's brother, laid siege to Stirling, which was held by Sir Philip Mowbray. Mowbray proposed a bargain: that he would surrender the castle, if it were not relieved by 24 June 1314. Bruce agreed, and withdrew. The following summer, the English duly headed north, led by Edward II, to save the castle. On 23–24 June, King Robert's forces met the English at the Battle of Bannockburn, within sight of the castle walls. The resulting English defeat was decisive. King Edward attempted to take refuge in the castle, but Mowbray was determined to keep to his word, and the English were forced to flee. Mowbray handed over the castle, changing sides himself in the process. King Robert ordered the castle to be slighted; its defences destroyed to prevent reoccupation by the English.