The Bulwark is an Iron Age fort located on the eastern end of Llanmadoc Hill. The site appears to have been developed over time, rather than built all at once. Three, one-metre high earth banks and ditches provide a line of defence around the fort with a causeway and entrance located on the eastern slope.
The Bulwark had a rectangular enclosure inside the earth banks. It is thought that the occupants of the fort were enemies with the occupants of hill forts on Harding Down. A local legend suggests that during one particularly gruesome battle, the blood from fallen warriors overflowed from their boots in such volumes that it filled up a lake – Tankey or Tonkin Lake, named after Tonkin their leader who was killed during the battle.