The tower was a particular triumph–it is the only 11th century great crossing tower still standing in England. Robert began with special thick supporting walls and four massive brick piers. The four-level tower tapers at each stage with clasping buttresses on the three lower levels and circular buttresses on the fourth stage. The entire structure weighs 5,000 tons and is 144 feet high. The tower was probably topped with a Norman pyramidal roof; the current roof is flat. The original ringing chamber had five bells, but none of them has survived.