THE FEUDAL LAND SYSTEM 247 diversity of their sites, to which the fortresses themselves were closely adapted. If the castle is perched on an in- 1 accessible peak, the circuit of its walls will be of an irregular ' shape following the edges of the summit and taking advan- i tage of every precipice and chasm. If the castle is built upon j comparatively level ground, it will be surrounded by a 1 deep moat full of water, so that the besiegers may not scale I its walls with ladders and movable towers, nor make breaches in them with battering-rams. Sometimes the cas- | tie is a single rectangular tower ; other castles are exten- "+*~i sive complexes of buildings and courtyards covering acres. I Some castles are in the heart of cities, some are in the fast- 1 nesses of the Alps, some line the banks of the Rhine' and of I many other rivers. A few common characteristics may be noted. One is the i prominence of towers, square, round, or pentagonal, with I pyramid ical, conical, or flat roofs. Some of these towers line the outer circuit of walls, projecting beyond them to enfilade their sides and bases, and rising above them to command their tops. Oldest and chief of the towers are the donjon, or residence of the lord, and the keep, or central and I most strongly fortified part of the castle where the garrison ! makes its last stand. Normally the defenders of the castle
- fight from the tops of its walls and towers, where they will
- be farthest away from the range of the missiles of the
i enemy below, and whence their own missiles will carry 1 farthest and fall with most force. For this purpose a walk is built behind a parapet all along the top of the wall. The battlements of the parapet are usually crenelated; that is, openings through which the defenders may shoot alternate with sections of solid wall behind which they may stand protected from the enemy's arrows. Sometimes, especially around the tops of towers, are found machicolations. In this case the battlement is built out beyond the walls of the tower below upon projections called corbels, and the floor of ! the encircling walk behind the parapet is pierced with num- erous openings or trapdoors through which such things as boiling pitch and molten lead may be poured directly upon
