The amphitheatre was built near the Porta Ticinese ("Ticino Gate") in the 2nd-3rd centuries AD, when Mediolanum grew as economical and political importance while Rome declined. It remained in use until the city was one of the capitals of the Western Roman Empire (4th or 5th centuries). Later it was abandoned after Christianism imposed the end to arena games, but also as, in the wake of the imperial crisis, animals to be used in the amphitheatre were no longer imported. It became a quarry for construction stones as early as the 4th century AD, when the Basilica of San Lorenzo was built. \ The edifice was demolished during a Barbarian attack to Milan, as it was located outside the walls and could therefore be used as stronghold by the attackers. The date of the event is however uncertain: it could be 402, during the Visigothic invasion of Italy, or in 452, when northern Italy was ravage by Attila, or during the Gothic Wars (6th century). http://en.wikipedia.org/wiki/Milan_amphitheatre