Cosimo I de' Medici has brought almost all of Tuscany under his rule; he is in 1569 created the first grand duke of Tuscany by Pope Pius V.

The Santa Trinita bridge built over the Arno by Bartolomeo Ammanati from 1567 to 1569, featuring three "basket-handled" arches that boast a rise-to-span ratio of only one to seven instead of the usual one to four, eclipses the mid-fourteenth century Ponte Vecchio still standing today.

The oldest elliptic arch bridge in the world, the three flattened ellipses give the structure its celebrated elegant appearance.

Its site, downstream of the equally remarkable Ponte Vecchio, is a major link in the medieval street plan of Florence, which has been bridged at this site since the thirteenth century.

The wooden bridge of 1252 had been swept away in a flood seven years later; rebuilt in stone, it was destroyed in a flood in 1333.

The bridge of five arches constructed by Taddeo Gaddi had been destroyed in the flood of 1557, which had occasioned Ammanati's replacement.