mast, large metal or timber pole secured vertically or nearly vertically in a ship, used primarily for supporting sails and rigging. The mast is as old as sailing vessels, and the oldest sailboats depicted (those of ancient Egypt) had a small mast placed forward and carrying a single sail. The Phoenician bireme had one mast, the Greek trireme had two. Viking ships had one central mast. In the Middle Ages, a topmast was added, fixed to the single mast, to carry more sail; after the 16th cent., topmasts were generally demountable. By that time the building of larger vessels and the desire for greater speed on longer journeys had already brought increase in sails and in the masts—a process that continued until the clipper ships of the middle of the 19th cent. were rushed forward by clouds of sails. Above the topmast was added the topgallant mast and above that the topgallant mast royal. In vessels having more than one mast, a small forward mast is called the foremast and a small mast abaft the mainmast is called the mizzenmast. A platform for lookout on a mast is called a crow's nest. The modern merchant ship often has a mast made of hollow steel tubes, which is used mainly for signaling and for supporting radio antennas and lifts or derricks for cargo. In some modern warships the mast has a steel platform on which are mounted instruments for controlling gunfire.