The foundation of Florence dates back to Roman times, despite evidence existing to show that Florence was already occupied in prehistoric times. The oldest part of the city bears the imprint of these Roman origins as it originated as one of Caesar's colonies. For the sake of defense, the city was set at the confluence of two streams, the Arno and the Mugnone, where the oldest populations had previously been located.
Rectangular in plan, it was enclosed in a wall about 1800 meters long. The built-up area, like all the cities founded by the Romans, was characterized by straight roads which crossed at right angles. The two main roads led to four towered gates and converged on a central square, the forum urbis, now Piazza della Repubblica, where the Curia and the Temple dedicated to the Capitoline Triad (Jupiter, Juno, and Minerva) were later to rise. Archaeological finds, many of which came to light during the course of works which "gave new life", to the old city center, have made it possible to locate and identify the remains of various important public works such as the Capitoline Baths, the Baths of Capaccio, the sewage system, the pavement of the streets and the Temple of Isis, in Piazza San Firenze. At that time the Arno was outside the walls, with a river port that constituted an important infrastructure for the city, for in Roman times the river was navigable from its mouth up to its confluence with the Affrico, upstream from Florence, and the first bridge in Florentine history was built in all likelihood somewhat upstream from today's Ponte Vecchio, around the first century B.C..
The city developed rapidly thanks to its favorable position and the role it played in the ambit of the territorial organization in the region and it soon superceded Arezzo as the leading center in northern Etruria. Economic power was the driving force behind the urban growth of the young colony. Commercial activity and trade thrived thanks to the fact that important communications routes, land and water, intersected at Florentia and offer an explanation for the presence of those oriental merchants, probably on their way from Pisa, who first introduced the cult of Isis and then, in the 2nd century, Christianity.
The earliest indications of the Christian religion are bound to the cults of the deacon Lorenzo and the Palestinian saint, Felicita and so the first Florentine churches were built: San Lorenzo consecrated in 393, the first diocese, and Santa Felicita, whose origins go back to the 4th and 5th centuries. However, the Florentines do not seem to have had a bishop prior to the late 3rd century. The first one recorded is San Felice who participated in a Roman synod in 313.