This was a cylindrical drill with circumferential saw teeth, similar to modern hole saws, which was used to drill a large hole into the patient’s skull. The drill was rotated by a bow string or a usually wooden handle. The drill was used to perform trepanations (its use is dated to the Paleolithic Age) to treat migraines, epilepsy and other mental disorders. Several patients survived trepanation, according to evidence supported by numerous healed trepanned skulls.