NOTES: Construction on the detached bell tower of the cathedral complex began in 1173 under the direction of Diotisalvi. The tower began to sink and lean after completion of the third storey in 1178. Building resumed in1272 under Giovanni di Simone, architect of the Campo Santo, but was interrupted again in 1284 on reaching the seventh storey, owing to further leaning. The belfry was added by Tommano Simone in 1350.