Mote and Baily Shell Keep Square Keep Concentric Castle. A Mote and Baily is basically a wooden palisade surrounded by a mote. It was very vulnerable to a fire. A shell keep replaced the wooded palisade on top of the mote with a thin stone wall. Wooden buildings were built inside, against the wall. You could still toss barrels of burning pitch over the wall to set the castle on fire. The square keeps were built of stone, the early ones were no more than just towers with thick walls. The defenders could fight off the attackers using arrows fired from the roof and from the window slits. The roofs often had crenelations along the edge to protect the defenders from the attackers' arrows. The attackers would use a battering ram to break through the walls. Later the towers were built circular, to deflect the battering rams and catapult and early artillery projectiles. Because most people are right handed, the spiral stairways inside the castles were built so that they spiraled to the right. The defender would presumably be fighting from the higher step, and he would have more room on his right to swing a sword, and could use the wall on his left for protection. The concentric castles had another wall surrounding a keep. The attacker would have to take the outer wall before attacking the inner keep, while the defender had a place to retreat and continue to fight. The outer wall was always lower than the inner keep so that the defender's archers could sweep the attackers off the outer wall from the safety of the inner keep. Towers were built along the wall at regular intervals and at key positions, such as around the gate. They provided strong points along the wall and places to mount catapults and later cannons and to provide access to the wall. If the attacker succeeded in climbing the wall in force, the defenders could retreat into the towers to isolate that portion of the wall, and continue to fight form the tower. Some of the larger castles had bastions outside the walls to protect the key approaches to the castle or to envelope the attacker with crossfire.