+CHURCH PLANS.+ The original basilica-plan underwent radical modifications during the 12th-15th centuries. These resulted in part from the changes in construction which have been described, and in part from altered ecclesiastical conditions and requirements. Gothic church architecture was based on cathedral design; and the requirements of the cathedral differed in many respects from those of the monastic churches of the preceding period. [Illustration: FIG. 111--BAR TRACERY, ST. MICHAEL’S, WARFIELD.] The most important alterations in the plan were in the choir and transepts. The choir was greatly lengthened, the transepts often shortened. The choir was provided with two and often four side-aisles, and one or both of these was commonly carried entirely around the apsidal termination of the choir, forming a single or double _ambulatory_. This combination of choir, apse, and ambulatory was called, in French churches, the _chevet_. Another advance upon Romanesque models was the multiplication of chapels--a natural consequence of the more popular character of the cathedral as compared with the abbey. Frequently lateral chapels were built at each bay of the side-aisles, filling up the space between the deep buttresses, flanking the nave as well as the choir. They were also carried around the _chevet_ in most of the French cathedrals (Paris, Bourges, Reims, Amiens, Beauvais, and many others); in many of those in Germany (Magdeburg, Cologne, Frauenkirche at Treves), Spain (Toledo, Leon, Barcelona, Segovia, etc.), and Belgium (Tournay, Antwerp). In England the choir had more commonly a square eastward termination. Secondary transepts occur frequently, and these peculiarities, together with the narrowness and great length of most of the plans, make of the English cathedrals a class by themselves. [Illustration: FIG. 112.--ROSE WINDOW, CHURCH OF ST. OUEN, ROUEN.] +PROPORTIONS AND COMPOSITION.+ Along with these modifications of the basilican plan should be noticed a great increase in the height and slenderness of all parts of the structure. The lofty clearstory, the arcaded triforium-passage or gallery beneath it, the high pointed pier-arches, the multiplication of slender clustered shafts, and the reduction in the area of the piers, gave to the Gothic churches an interior aspect wholly different from that of the simpler, lower, and more massive Romanesque edifices. The perspective effects of the plans thus modified, especially of the complex choir and _chevet_ with their lateral and radial chapels, were remarkably enriched and varied.