A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity. The first guns were made in a time where metallurgy was not advanced enough to cast tubes able to withstand the explosive forces of early cannon, so the pipe (often actually built from staves of metal) needed to be braced periodically along its length, producing an appearance somewhat reminiscent of a storage barrel. Another explanation, tied to etymology, states that many very first firearms barrels were in fact realized, during the 12th and 13th centuries, using small storage barrels with their usual metal rings reinforced by leather, hence the barrel name