The outer bailey of Kenilworth Castle is usually entered through Mortimer's Tower, today a modest ruin but originally a Norman stone gatehouse, extended in the late 13th and 16th centuries. The outer bailey wall, long and relatively low, was built mainly by King John; it has numerous buttresses but only a few towers, being designed to be defended primarily by the water system of the Great Mere and Lower Pool. The north side of the outer bailey wall was almost entirely destroyed during the slighting. Moving clockwise around the outer bailey from Mortimer's Tower, the defences include a west-facing watergate, which would originally have led onto the Great Mere; the King's gate, a late 17th-century agricultural addition; the Swan Tower, a late 13th-century tower with 16th-century additions, then named after the swans that lived on the Great Mere; the early 13th-century Lunn's Tower; and the 14th-century Water Tower, so named because it overlooked the Lower Pool.