Tracery is the ornamental stonework — bars, ribs and cusps — that divides and decorates a Gothic window. It evolved from the earliest Gothic period in 12th-century France, when architects began cutting geometric patterns from the stone infill of windows (plate tracery), to the more elaborate 'bar tracery' of the 13th century, where slender stone bars create complex geometric patterns — circles, lozenges, trefoils, quatrefoils. The great west windows of Lincoln Cathedral, the rose windows of Notre-Dame de Paris and Chartres Cathedral, and the Rayonnant Gothic façades of the 13th century demonstrate how tracery transformed Gothic architecture from stone structure into a screen for stained glass. Later Flamboyant Gothic tracery (15th century) used flame-shaped ogee curves of extraordinary complexity. The patterns of Gothic tracery were revived in the 19th-century Gothic Revival and can be seen in everything from wallpaper to cast-iron fencing.