A brigantine was a two-masted sailing vessel with a fully square-rigged foremast and at least two sails on the main mast: a square topsail and a gaff sail mainsail (behind the mast). The main mast is the second and taller of the two masts. By the first half of the 18th century the word had evolved to refer not to a kind of vessel, but rather to a type of rigging: two-masted, with her foremast fully square-rigged and her mainmast rigged with both a fore-and-aft mainsail (a gaff sail) and square topsails and possibly topgallant sails. During the Age of Sail, brigs were fast and manoeuvrable and were used as both naval warships and merchant vessels. They were especially popular in the 18th and early 19th centuries. Brigs fell out of use with the arrival of the steam ship because they required a relatively large crew for their small size and were difficult to sail into the wind.