The construction was carried out, unusually, from the west to the east, beginning in the nave. De Cormont gave the structure its striking dimensions and harmony by his construction of the grand arcades and the upper windows. The nave was completed in 1236, and by 1269, the upper windows of the choir were in place. At the end of the 13th century, the arms of the transept were completed, and in the beginning of the 14th century the facades and the upper towers were finished. While these works underway, the chapels between the buttresses and at the angles of the transept were added.