In 59 BC, Roman soldiers settled in Florentia, present-day Florence. The Roman Emperor himself awarded his army veterans the fertile land of the Arno river valley, where they built an army camp. The pattern of the camp was typical of Roman castrums (military camps) and can be seen in the city centre today. The main streets of Florentia intersected at today's Piazza della Repubblica.

Florentia laid on the major strategic route between Rome and the north, enabling it to expand and become an important trade centre. In the 3rd Century AD, the town was made the capital of Tuscia province by Emperor Diocletian. The city’s first martyr was St Minias, who was decapitated during Emperor Decius’ persecutions of Christians. His heritage is preserved at the Basilica di San Miniato al Monte, which was built where he was beheaded.

Other significant Christian saints of Florentia include St Lorenzo and St Felicita. The first churches in Florentia were built in their honour, namely San Lorenzo, which was consecrated in AD 393 as the first diocese, and Santa Felicita, at the turn of the 4th and 5th Centuries. However, Florentines did not have a bishop until the end of the 3rd Century, recorded in San Felice and participant of a Roman synod in AD 313.