The crossword solution for the term SURROUND, AS A CASTLE is BESIEGE, which has 7 letters. BESIEGE is a military tactic in which an attacking force surrounds a defended location in order to isolate it and prevent supplies and reinforcements from entering or leaving. This tactic was often used in the Middle Ages when besieging a castle, as the attackers would surround the castle with troops and equipment in order to starve out the defenders.