After 1375, the west front had to be reinforced by a new buttress, and several of the vaults of the nave had to be rebuilt. In 1427, an earthquake caused serious damage to the structure, and in 1527, the vaults of the north transept had to be rebuilt. In 1516 lightning struck the bell tower, causing debris to fall onto the roof of the chapel of the Holy Crucifix below. Some modifications were made to the Romanesque features; larger windows were installed north transept, and in the adjoining parts of the nave. The whole complex suffered from a lack of maintenance; roofs leaked, damaging the masonry of the vaults below.