sentences:  He was replaced by Mirabel de Gordon, whose performance at Stirling was regarded as so incompetent, some suspected he had been bribed.The besiegers opened fire on 20 March but poor roads and lack of horses to pull them meant the heavy guns remained at Inverness; the light guns and mortars available made minimal impression on the walls.In accordance with then prevailing rules of war, the garrison was summoned to surrender on 22 March; unsurprisingly, Scott refused, telling them he would defend the place to 'the last extremity'.