In general, Bremen Cathedral is a medieval building. The oldest visible structures are the two crypts. The last parts built in romanesque style and in sandstone were the lower storeys of the western façade and the western towers. Since the late 1220s, vaults and walls were erected in bricks, partly hidden by sheets of sandstone. Only the outer wall of the southern row of chapels shows unhidden bricks. St Peter's is one of the largest historic brick structures in Europe, but it comprises too many stone structures to be subsumed to Brick Gothic. During the great restoration of 1888 to 1901, the western towers and most of the western façade were rebuilt relatively close to previous structures. The crossing tower was a new addition, using the medieval crossing tower of Worms Cathedral as an example. The roofs above the transepts and the northern aisle were redesigned.