Berwick-upon-Tweed. Six weeks later a large English army under Edward III joined them, bringing the total number of besiegers to nearly 10,000. Grosmont was present at the siege, but it is not known if he marched with his father-in-law and Balliol, or with the main English effort. The Scots felt compelled to attempt to relieve the siege and an army of 20,000 men attacked the English at the Battle of Halidon Hill, from Berwick. Under intense bow-fire the Scottish army broke, the camp followers made off with the horses and the fugitives were pursued by the mounted English knights. Scottish casualties were numbered in thousands, including their commander and five earls dead on the field. Scots who surrendered were killed on Edward's orders and some drowned as they fled into the sea. English casualties were reported as fourteen; some chronicles give a lower figure of seven. About a hundred Scots who had been taken prisoner were beheaded the next morning, 20July. It is presumed that Grosmont took part in the battle, but it is possible that he was part of the detachment posted to ensure that the garrison of Berwick did not sally. Berwick surrendered the day after the battle and Grosmont witnessed and sealed the articles of surrender and, a little later, the town's new charter. Having sworn fealty to David II and because Balliol intended to make Scotland subservient to the English, most Scots refused to accept Balliol as their monarch. In December 1334 Grosmont accompanied Edward III to Roxburgh in Scotland. The English force of 4,000 accomplished little and withdrew in February. Grosmont was a member of Edward III's negotiation team when a brief truce was agreed shortly after at Nottingham. In July Grosmont accompanied Edward III on another invasion of Scotland, with an army of 13,000for the time an extremely large force. Scotland was quelled as far north as Perth and Grosmont took a senior role in raiding deeper into the country. In 1336 Grosmont was given command of 500 men-at-arms and 1,000 longbowmen and marched to Perth. Informed that the widow of the Earl of Atholl was besieged in Lochindorb Castle, Grosmont led a small force to rescue her and raise the siege, which he had achieved by 16 July. He was given full plenipotentiary powers by the King. After Edward III reached Perth with the main English army, Grosmont was despatched on a long-range