control, Milan was declared the capital of the Western Roman Empire by Emperor Diocletian in 293 AD. Diocletian chose to stay in the Eastern Roman Empire (capital Nicomedia) and his colleague Maximianus ruled the Western one. Immediately Maximian built several gigantic monuments, like a large circus 470 × 85 m (1,540 ft × 279 ft), the Thermae Herculeae, a large complex of imperial palaces and several other services and buildings.
With the Edict of Milan of 313, Emperor Constantine I guaranteed freedom of religion for Christians. The city was besieged by the Visigoths in 402, so the imperial residence was moved to Ravenna. In 452, the Huns overran the city. In 539, the Ostrogoths conquered and destroyed Milan in the course of the so-called Gothic War against Byzantine Emperor Justinian I. In the summer of 569, the Longobards (from which the name of the Italian region Lombardy derives), a Teutonic tribe conquered Milan, overpowering the small Byzantine army left for its defence. Some Roman structures remained in use in Milan under Lombard rule. Milan surrendered to the Franks in 774 when Charlemagne, in an utterly novel decision, took the title "King of the Lombards" as well (before then the Germanic kingdoms had frequently conquered each other, but none had adopted the title of King of another people). The Iron Crown of Lombardy dates from this period. Subsequently Milan become part of the Holy Roman Empire.
Middle Ages
During the Middle Ages, Milan prospered as a centre of trade due to its command of the rich plain of the Po and routes from Italy across the Alps. The war of conquest by Frederick I Barbarossa against the Lombard cities brought the destruction of much of Milan in 1162. After the founding of the Lombard League in 1167, Milan took the leading role in this alliance. As a result of the independence that the Lombard cities gained in the Peace of Constance in 1183, Milan became a duchy. In 1208 Rambertino Buvalelli served a
