Stone walls are usually made of local materials varying from limestone and flint to granite and sandstone. However, the quality of building stone varies greatly, both in its endurance to weathering, resistance to water penetration and in its ability to be worked into regular shapes before construction. Worked stone is usually known as ashlar, and is often used for corners in stone buildings. Granite is very resistant to weathering, while some limestones are very weak. Other limestones, such as Portland stone, are more weather-resistant.
Large structures are usually made of very thick walls, so that castles and cathedrals possess walls which may be up to 12 feet thick. They normally consist of a layered stone exterior and rubble infill.