Masts, the nearly perpendicular timbers, or steel tubes, to which are attached the rigging, yards, and sails of a ship. A mast is either of one piece, in which case it is a "pole-mast," or it is composed of several sections, each of which also retains for itself the name of mast, and each of which, if large, may, in turn, be built up of several timbers. When a vessel has two masts, the foremost is the foremast, and the aftermost the main. Where there are three, the foremost is the foremast, the middle is the main, and the aftermost is the mizen. Each of these masts may consist of as many as four principal sections raised one above the other, and known, respectively, as the lower mast, the top-mast, the topgallant mast, and (though this is a rare addition) the topgallant-royal mast. Extra masts aft of the mizen are termed jiggers or spankers. Lower masts are now very generally made of iron or steel. In days when ships depended exclusively, or even chiefly, on sail power, the dimensions of masts were generally larger than at present.