Saxon Switzerland is characterized by its sandstone rocks which draw many rock climbers. There are some 14,000 climbing routes on over 1,100 rock pinnacles. At the beginning of the 20th century, the Saxon Rules for rock climbing were established. They are considered to be one of the origins of free climbing. Ropes and bolts may only be used for safety but never as a means of climbing. The use of chalk and common means of protection such as nuts and friends is also not permitted; instead knotted nylon slings are used. With a few exceptions, climbing is only practised and permitted at freestanding rock towers.