The genesis of the shot put can be traced to pre-historic competitions with rocks: in the Middle ages the stone put was known in Scotland and the steinstossen was recorded in Switzerland. In the 17th century, cannonball throwing competitions within the English military provided a precursor to the modern sport. The term "shot" originates from the use of round shot-style ammunition for the sport. The modern rules were first laid out in 1860 and required that competitors take legal throws within a square throwing area of seven feet (2.13 m) on each side. This was amended to a circle area with a seven-foot diameter in 1906, and the weight of the shot was standardised to 16 pounds (7.26 kg). Throwing technique was also refined over this period, with bent arm throws being banned as they were deemed too dangerous and the side-step and throw technique arising in the United States in 1876.