of the new structure was not planned to be higher than 30–35 meters. The plan integrated the neighbouring Collegiate church of Our Lady into the western end of the cathedral, which resulted in the absence of a traditional west-end portal. The south-western porch of the cathedral became the entrance of the former collegiate church. The nave, with the exception of its vaults, was probably finished between 1245 and 1250. Then a decision was taken to make the cathedral much taller, with the addition of a new level of large windows about forty meters high, equal in height to the two levels below. New more massive columns were added, and the triforium between the arcades and high windows was enlarged and strengthened to support the greater weight. Between 1250 and 1255 the south side walls west of the transept were also strengthened to support the new higher walls. The south façade was also built higher to match the greater height of the new nave. The piers of the flying buttresses were also reconstructed, doubling their height. In about 1270–75, the tower of the Chapter was raised to the height of the cornice of the new nave. Since the new nave was now twice as high as planned, the towers also had to be made taller. Between 1275 and 1280, A second level and the beginning of a third level were added to the Tour de la Mutte. By 1359 the nave was entirely covered, but work on the upper walls continued for another twenty years. In 1380–81, the canons of the cathedral decided to demolish the wall which separated the cathedral from the adjoining nave of the church of Our Lady. This was resisted by the clergy of the collegiate church, but the work went ahead, modified by the installation of a grill between the two naves. In 1381 the cathedral chapter engaged the glassmaker Herman of Münster to make a rose window for the west front, which was finished in 1392. There was a lull of nearly a century before major work was resumed on the construction of the transept and the choir. In 1388 a wooden belfry was installed by the city government on the La Mutte tower, and a new chapel, the Bishop's Chapel, was added on the lower south aisle in 1443. Its patron, Bishop Conrad Bayer of Boppard, died a few days after the chapel was