"A variety of material was used in the construction of a medieval concentric castles. The most important was of course stone which could be mined in quarries. Stone in several of these medieval castles was also used from the ruins of old Roman fortifications. Other materials that were commonly used in the construction of concentric castles included hard chalk, flint stone, sandstone, and limestone. Lime mortar was used to keep the stones in place and consisted of a mixture of water, coal, and lime."