Related Clues:

• Fortification ditch
• Gunner's enclosure
• Water under the bridge?
• Castle's protective device
• Defensive trench
• Means of defense, once
• Ring of water
• Medieval protection against invasion
• Wall alternative, perhaps
• Medieval invader's obstacle
• Zoo construction
• Defensive ring
• Tower-like projection on defensive wall.
• Tower for a gun protection
• .Ditch around a castle