Possible Clues:

• Ancient Roman stone thrower
• Ancient siege weapon for launching stones
• Shelf inside a flap that's raised in old weapon
• Medieval siege catapult
• Ancient siege weapon
• Ed volunteers to carry one ancient projector
• Everything is protected by British army's military device
• Catapult found in Welsh lake stretching across border
• Catapult series of items into Welsh lake
• Ancient weapon set down in Welsh lake