The post horn (also posthorn, post-horn, or coach horn) is a valveless cylindrical brass or copper instrument with cupped mouthpiece, used to signal the arrival or departure of a post rider or mail coach. It was used especially by postilions of the 18th and 19th centuries. Mail coaches had tight schedules and travelled at high speed, given priority of way in most countries. Other road users were required to clear completely out of the way.