 The high and thin walls of French "Rayonnant Gothic" allowed by the flying buttresses enabled increasingly ambitious expanses of glass and decorated tracery, reinforced with ironwork.This first 'international style' was reflected in the clerestory of Metz Cathedral ("c".1245–), then Cologne's cathedral ("c".1250–), and again in the nave of the cathedral at Strasbourg ("c".1250–).Masons elaborated a series of tracery patterns for windows – from the basic "geometrical" to the "reticulated" and the "curvilinear -" which had superseded the lancet window.