Political map of Europe & the Mediterranean late 258 (First Alemannic Invasion of Italy): Struggling to defend both the Rhine and Danube frontiers, Gallienus was caught off guard when the Alemanni managed to cross the Alps into Italy in 258. The Senate (Roman Senate) hurriedly organized the defence of Rome, giving Gallienus time to enter Italy and defeat the invaders at Mediolanum (Milan) in 259 (Battle of Mediolanum). The incident, however, demonstrated that now even Rome was vulnerable to barbarian incursions.