Tracery is one of the most characteristic design elements of Gothic architecture, developing from the early 13th century in France. It refers to the intricate subdivision of large window openings by delicate stone ribs into geometric forms such as cusps, foils, flowing curves, and rosettes. The progressive dissolution of the wall in favor of large glazed surfaces made tracery structurally necessary to stabilize the glass infill. At the same time, it became a vehicle for Gothic aesthetics: the complex, repeating patterns symbolized heavenly order and divine geometry. From simple arched windows to enormous rose windows, tracery developed an extraordinary formal diversity that defines cathedrals such as Notre-Dame de Paris and Cologne Cathedral.