The scarce archaeological evidence trace the foundation of Milan, as a small village, in the sixth century B.C.
According to a legendary tradition, reported by Tito Livio in 600 B.C.,  about Belloveso, a prince from Gaul, after defeating the Etruscans near the Ticino river, would set aside, with the consent of the Celts Insubri that already lived in the area, in a clearing where Belloveso saw a sow wild  “half-wolly” boar that he interpreted as a divine omen for his inauguration, which he called “Mediolanum” (Medio-lana). The memory of this legend is visible in Piazza Mercanti, the medieval Lombard region palace, where you can see a bas-relief depicting that identify an “half-wolly” boar: medio-lana.
Piazza Mercanti is certainly worth visiting as the beating heart of the medieval city.
Milan remained for many centuries a small village without defensive walls (as Polybius wrote).
Mediolanum was in conflict with the Romans from 222 B.C. and it was finally subdued in 77 B.C. and in 49 was elevated to the rank of “Municipium Civium Romanorum” (as well as other cities of Lombardy).

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The oldest urban Roman testimonials  of  Milan seem to be the remains of the theater, that we assume to have a capacity of 7,000 spectators and it is accessible (in the case of reservation) in 14, Via S. Vittore at the theater  (headquarters of the Chamber of Commerce of Milan).