How Much of the Florence Baptistery is a Surviving Roman Building?

Arguably the most enigmatic building in the city, the famous octagonal Baptistery in Florence has given rise to more debate on archaeological, architectural and artistic grounds than probably any other building in all of Italy. A span of some thousand years, from the fifth to the fifteenth centuries, separates the periods to which the building we see today has been variously and confidently ascribed. Gathering the available evidence and weighing the merits of the theories put forward in the past, the author opts for the building's completion in the thirteenth century, arguing that there were two San Giovannis, a small Baptistery built in front of the fifth-century first cathedral of Santa Reparata, and its eleventh-century Romanesque successor, a much enlarged rebuilding of it, designed for defence in perilous times of civil strife, and later by the thirteenth century graced by today's colourfully bright marble decoration.