In his 1919 book Ad Quadratum, Frederik Macody Lund, a historian who studied the geometry of several gothic structures, claims that the Cathedral of Chartres (begun in the 12th century), the Notre-Dame of Laon (1157–1205), and the Notre Dame de Paris (1160) are designed according to the golden ratio. According to Macody Lund, the superimposed regulator lines show that the cathedral has golden proportions. Other scholars argue that until Pacioli's 1509 publication, the golden ratio was unknown to artists and architects.