ROSE WINDOW or WHEEL WINDOW, in architecture, a term applied to any decorated, circular window. Undecorated circular windows are found in certain imperial Roman structures, used especially in the upper portions of rooms or pierced through vaults, as in the tomb of the time of Hadrian known as the Casale dei Pazzi, near Rome, but structural decoration of such forms was apparently not attempted until the Byzantine and Roman esque periods. One of the earliest decorated circular windows extant is that of the Italian Romanesque church of S. Maria in Pomposa, possibly as early as the loth century, in which the deco ration consists of a pierced marble slab of great richness, with a design of interlaces and birds purely Byzantine. In French Romanesque work circular windows also appear, but in the earlier examples, such as the iith century apse of S. Sernin at Toulouse, they are undecorated, like those of the Roman empire. Mean while, in Mohammedan work, the cusped circle had been a corn mon form, usually, however, not as a window, but as the outer boundary of a sunk hemisphere, as in the mosque of Ibn Touloun at Cairo (876-78).
The crusaders probably saw many examples of such forms ; in any case it is only after the earlier crusades and especially towards the middle of the 12th century that the idea of making a rich decorative motive out of a round window appeared. From then on the simple rose window became more and more common, and was, in fact, a distinguishing characteristic of many transitional and early Gothic cathedrals. It was particularly used at the west end of the nave and the ends of the transepts. An exceptional early use is the round window which lighted the triforium roof space from the nave in the original form of Notre Dame at Paris (before 1177). In the west front of Laon cathedral (completed prior to 1200) there is an enormous rose window with 12 semi circles around the edge and the central foiled and cusped circle separated from the apexes of these semi-circles by a considerable distance, the connection between being made by little radiating colonnettes like spokes. This window is remarkably advanced for its date, as the filling, like that of the Paris triforium, is es sentially bar tracery. The rose window of the west front of Char tres cathedral (1194-1212) consists, on the other hand, of plate tracery, the circle being filled with a thin plate of stone, through which are pierced many small foiled or cusped holes. A similar
form of plate tracery within a circle is used to cap the twin windows of the clerestorey bays.
The introduction of developed bar tracery gave a compelling impetus to rose window design. The general scheme consisted of a series of radiating forms, each of which was tipped by a pointed arch at the outside of the circle. The bars between these forms were joined at the centre by a pierced circle of stone and the forms themselves frequently treated like little traceried windows with subsidiary, subdividing bars, arches and foiled circles. The most beautiful examples of this type are those of the west front of Rheims cathedral (end of the 13th century) and the transepts of Rheims, Amiens and Notre Dame at Paris (all of the last half of the 13th century). The introduction of the wavy lines of flamboyant tracery completely changed the character of French rose windows, but they continued basically radiating in design. The radiating elements consisted of an intricate network of wavy, double curved bars, creating all sorts of interesting circles and flame shapes, and incidentally, furnishing a diagonal bracing to the whole composition which added materially to its structural strength. The rose at the end of the transept at Beauvais (early 16th century) is characteristic.
The influence of the French rose windows was widespread from an early period. Variations of the form appear in a multitude of late Italian Romanesque churches, as in the widely varying type in the late 12th century west front of S. Pietro in Toscanella, and the more normal example in S. Zeno at Verona (late 12th century). In England the rose window has never been so popular as in France. Those in the transepts of Westminster Abbey are more characteristically French than English. The most typi cally English examples are in the transepts of Lincoln cathedral; that on the north from the Early English period is a remarkably delicate example of plate tracery; that on the south from the Curvilinear period of the early 14th century is striking because it is not radiating in design, and therefore completely at odds with the French prototypes. (See TRACERY.) (T. F. H.)