The exterior was even more radically transformed by these changes, and by the addition of towers and spires to the fronts, and sometimes to the transepts and to their intersection with the nave. The deep buttresses, terminating in pinnacles, the rich traceries of the great lateral windows, the triple portals profusely sculptured, rose-windows of great size under the front and transept gables, combined to produce effects of marvellously varied light and shadow, and of complex and elaborate structural beauty, totally unlike the broad simplicity of the Romanesque exteriors. [Illustration: FIG. 113.--FLAMBOYANT DETAIL FROM PULPIT IN STRASBURG CATHEDRAL.] [Illustration: FIG. 114.--EARLY GOTHIC CARVING.] +DECORATIVE DETAIL.+ The mediæval designers aimed to enrich every constructive feature with the most effective play of lights and shades, and to embody in the decorative detail the greatest possible amount of allegory and symbolism, and sometimes of humor besides. The deep jambs and soffits of doors and pier-arches were moulded with a rich succession of hollow and convex members, and adorned with carvings of saints, apostles, martyrs, and angels. Virtues and vices, allegories of reward and punishment, and an extraordinary world of monstrous and grotesque beasts, devils, and goblins filled the capitals and door-arches, peeped over tower-parapets, or leered and grinned from gargoyles and corbels. Another source of decorative detail was the application of tracery like that of the windows to wall-panelling, to balustrades, to open-work gables, to spires, to choir-screens, and other features, especially in the late fourteenth and fifteenth centuries (cathedrals of York, Rouen, Cologne; Henry VII.’s Chapel, Westminster). And finally in the carving of capitals and the ornamentation of mouldings the artists of the thirteenth century and their successors abandoned completely the classic models and traditions which still survived in the early twelfth century. The later monastic builders began to look directly to nature for suggestions of decorative form. The lay builders who sculptured the capitals and crockets and finials of the early Gothic cathedrals adopted and followed to its finality this principle of recourse to nature, especially to plant life. At first the budding shoots of early spring were freely imitated or skilfully conventionalized, as being by their thick and vigorous forms the best adapted for translation into stone (Fig. 114). During the thirteenth century the more advanced stages of plant growth, and leaves more complex and detailed, furnished the models for the carver, who displayed his skill in a closer and more literal imitation of their minute veinings and indentations (Fig. 115). This artistic adaptation of natural forms to architectural decoration degenerated later into a minutely realistic copying of natural foliage, in which cleverness of execution took the place of original invention.