Dating back to around the sixth century, this is Florence's oldest building.
It is though that the beginnings of a baptistery for St John on this site were from around the sixth century (although records aren't able to say for certain). The building is thought to have been developed in its current octagonal form even at that time, and was built next to the then cathedral, Santa Reparata.
Between the 11th and 16th century the Battistero was embellished and expanded and had the now world-famous three sets of doors attached along with the surrounding marble statues, engravings and bronzes.
Nowadays visitors can still see replicas of the famous bronze doors as well as many other original details. There are 13th century mosaics on display as well as the font where Dante was baptised.
Map showing the location of Battistero di San Giovanni Piazza Duomo