Rayonnant style (rāˈənănt) [key], the middle period (c.1240–1350) of French Gothic architecture, so termed from the characteristic radiating tracery of the rose window. In this period many of the great cathedrals were under construction; the builders became bolder and more proficient, emphasizing in every way the vertical elements of the structure. Light and soaring structural skeletons were erected, reducing the size of all supporting members; the enlargement of windows resulted in a drastic reduction of wall surfaces. Bar tracery, displaying elaborate geometrical patterns, supplanted plate tracery. Sculptural ornament turned to greater naturalism and was used more generously. Of this period are the cathedral at Amiens (begun 1220), the Sainte-Chapelle at Paris (1243–46), and the earlier portions of St. Ouen at Rouen (begun 1318). The Rayonnant style spread to other parts of Europe. The scheme was employed in the cathedrals at Cologne, Germany (begun 1248), and Leon, Spain (begun c.1255).