In order to build strong, durable structures that can pass the test of time and the elements, stone is often used. It is unequaled in sheer strength, except for materials that are impractical to use as building materials. Castles and keeps, and other buildings that require protection from more then just the elements have used stone as the basic building element for quite some time. Its resistance, but not invulnerabilty, to fire is its strongest asset. Due to its desireable features of strength, and durability, it is also a difficult material to work with. Choosing the right stone and shaping it takes much skill.