The identity of the Tower of Pisa’s first architect remains a mystery. For many years, the initial phase of the design work was attributed to Bonanno Pisano, a well-known 12th-century resident artist of Pisa. However, recent studies appear to indicate that an architect named Diotisalvi, who designed the baptistery, was also responsible for the tower. The second phase of construction is attributed to Giovani di Simone, who added four floors to the tower in 1275. Architect Tommaso di Andrea Pisano (1350-1372) was the architect who finished the work and succeeded in harmonizing the Gothic elements of the bell-chamber with the Romanesque style of the tower.