TIE.--A beam of wood, bar of iron, or similar expedient employed to hold together the feet or sides of an arch, vault, or roof, and so counteract the thrust. TORUS.--A large convex moulding. TOWER.--A portion of a building rising conspicuously above the general mass, and obviously distinguished by its height from that mass. A detached building of which the height is great, relative to the width and breadth. TRACERY (Gothic).--The ornamental stonework formed by the curving and interlacing of bars of stone, and occupying the heads of windows, panels, and other situations where decoration and lightness have to be combined. The simplest and earliest tracery might be described as a combination of openings pierced through the stone head of an arch. Cusping and foliation (which see) are features of tracery. (See Figs. 18, 19, 55, and 57 in the text.) [Illustration: FIG. _E E_.--PERPENDICULAR WINDOW-HEAD.] [Illustration: FIG. _F F_.--LATE PERPENDICULAR WINDOW-HEAD.] TRANSEPT.--The arms of a church or cathedral which cross the line of the nave. TRANSITION.--The architecture of a period coming between and sharing the characteristics of two distinctly marked styles or phases of architecture, one of which succeeded the other. TRANSOM.--A horizontal bar (usually of stone) across a window or panel. TREFOIL.--A three-leaved or three-lobed form found constantly in the heads of windows and in other situations where tracery is employed. TRIFORIUM (or THOROUGH-FARE).--The story in a large church or cathedral intermediate between the arcade separating the nave and aisles, and the clerestory. TUDOR.--The architecture of England during the reigns of the Tudor kings. The use of the term is usually, however, restricted to a period which closes with the end of Henry VIII.'s reign, 1547. TURRET.--A small tower, sometimes rising from the ground, but often carried on corbels and commencing near the upper part of the building to which it is an appendage. TYMPANUM.--The filling in of the head of an arch, or occasionally of an ornamental gable. UNDERCUTTING.--A moulding or ornament of which the greater part stands out from the mouldings or surfaces which it adjoins, as though almost or quite detached from them, is said to be undercut. VAULT.--An arched ceiling to a building, or part of a building, executed in masonry or in some substitute for masonry.