 As with modern land mines, they were "victim-operated", often concealed, and formed zones that were wide enough so that the enemy could not do much harm from outside, but were under fire (from spear throws, in this case) if they attempted to remove the obstacles.A notable use of these defenses was by Julius Caesar in the Battle of Alesia.His forces were besieging Vercingetorix, the leader of the Gauls, but Vercingetorix managed to send for reinforcements.