Milan’s heritage as a capital city reaches back to antiquity. The Gauls settled in the Po Plain region, driving out the Etruscans around 400 BC. They founded a city but it was captured by the Romans in 222 BC and integrated into the Roman Empire. The Romans named this city Mediolanum. Following a series of revolts, it was brought under Latin rule in 89 BC. In 15 BC, the city became the regional capital and was called Roma Secunda, due to its strategic location. In AD 313, Roman Emperor Constantine issued an edict of tolerance toward Christians, and afterwards many churches were built in the city, including the Church of St Ambrogio, named after its first bishop, who was consecrated as a saint after his death. Today, St Ambrose is the patron saint of the city.

In AD 569, the city was conquered by the Lombards. In the late 8th Century, the bishops formed an alliance with the emperors, and their power increased considerably, which was augmented by Ottone of Saxony, whose coronation as King of Italy took place in the Church of St Ambrogio.