 Plate tracery, in which lights were pierced in a thin wall of ashlar, allowed a window arch to have more than one light - typically two side-by-side and separated by flat stone spandrels.The spandrels were then sculpted into figures like a roundel or a quatrefoil.Plate tracery reached the height of its sophistication with the 12th century windows of Chartres Cathedral and in the "Dean's Eye" rose window at Lincoln Cathedral.