 By the 1860s it had been re-armed with eighteen 18-pounder carronades, twenty 12-pounder carronades and ten 8-inch mortars.The Drop Redoubt is one of the two forts on Western Heights, and is linked to the other, the Citadel, by a series of dry moats (the lines).It is, arguably, the most impressive and immediately noticeable feature on Dover’s Western Heights.