The solid, massive building is enhanced by the simple tower with its clock. Giovanni Villani wrote that Arnolfo di Cambio incorporated the ancient tower of the Foraboschi family (the tower then known as "La Vacca" or "The Cow") into the new tower's facade as its substructure; this is why the rectangular tower (height 94 m) is not directly centered in the building. This tower contains two small cells, that, at different times, imprisoned Cosimo de' Medici (the Elder) (1435) and Girolamo Savonarola (1498). The tower is named after its designer "Torre d'Arnolfo". The tower's large, one-handed clock was originally constructed in 1353 by the Florentine Nicolò Bernardo, but was replaced in 1667 with a replica made by Georg Lederle from the German town of Augsburg (Italians refer to him as Giorgio Lederle of Augusta) and installed by Vincenzo Viviani.