Cities sometimes identified (often erroneously) churches dedicated to their patron saint with pagan temples. According to Chrétien, the ruling Guelph party favored San Giovanni because of his association with Florences Roman origins, and Florentines believed that the eleventh century Baptistery of San Giovanni had once been a pagan temple dedicated to the Roman war god, Mars. Florentine historian Vincenzo Borghini (1515-1580) wrote in the sixteenth century that the Baptistery was originally built as a temple to Mars, part of the proliferations of these temples in the provinces during the time of the Emperor Augustus, who erected the Temple of Mars Ultor in Rome
to commemorate his victory over Mark Anthony and the assassins of Julius Caesar.
Borghini illustrated a reconstruction of the old temple in his treatise on the Roman origins of Florence, believing that the Christians had later converted the temple into a church, just as had been done in Rome to the Pantheon.
