Mediolanum, the ancient city where Milan now stands, was originally an Insubrian city, but afterwards became an important Roman city in Northern Italy.

The city was settled by a Celtic tribe belonging to the Insubres group and belonging to the Golasecca culture under the name Medhelanon around 590 BC, conquered by the Romans in 222 BC, who Latinized the name of the city into Mediolanum, and developed into a key centre of Western Christianity and informal capital of the Western Roman Empire. It declined under the ravages of the Gothic War, its capture by the Lombards in 569, and their decision to make Ticinum the capital of their Kingdom of Italy.

During the Principate the population was 40,000 in AD 200; when the city became capital of the Western Roman Empire under emperor Maximian (r. 286–305), the population rose to 100,000 people and thus Milan became one of the largest cities in Roman Italy.

The city was settled by a Celtic tribe belonging to the Insubres group and belonging to the Golasecca culture around 590 BC under the name Medhelanon According to the legend reported by Livy, the Gaulish king Ambicatus sent his nephew Bellovesus into northern Italy at the head of a party drawn from various Gaulish tribes; this Bellovesus was said to have founded Mediolanum (in the time of Tarquinius Priscus, according to this legend).