defense of the empire. He took up arms against the Franks in 300 or 301 and in 302 – while Maximian was resting in Italy – continued to campaign against Germanic tribes on the Upper Rhine. According to Aurelius Victor, he also built a palace near his home town of Sirmium. In addition to the imperial palace in Sirmium another palace has been found at Glac, which may be that of Maximian. Retirement Diocletian's vicennalia, the 20-year anniversary of his reign, was celebrated in Rome in 303. Some evidence suggests that it was then that Diocletian exacted a promise from Maximian to retire together, passing their titles as Augusti to the Caesars Constantius and Galerius. Presumably Maximian's son Maxentius and Constantius's son Constantine – children raised in Nicomedia together – would then become the new Caesars. While Maximian might not have wished to retire, Diocletian was still in control and there was little resistance. Before retirement, Maximian would receive one final moment of glory by officiating at the Secular Games in 304. On 1 May 305, in separate ceremonies in Milan and Nicomedia, Diocletian and Maximian retired simultaneously. The succession did not go entirely to Maximian's liking: perhaps because of Galerius' influence, Galerius' former army comrade Severus and Galerius' nephew Maximinus (both of whom had long military careers) were appointed Caesar, thus excluding Constantine and Maxentius. Maximian quickly soured to the new tetrarchy, which saw Galerius assume the dominant position Diocletian once held. Although Maximian led the ceremony that proclaimed Severus as Caesar, within two years he was sufficiently dissatisfied to support his son's rebellion against the new regime. Diocletian retired to the expansive palace he had built in his homeland, Dalmatia near Salona on the Adriatic. Maximian retired to villas in Campania, Lucania or Sirmium, where he lived a life of ease and luxury. Although far from the political centers of the Empire, Diocletian and Maximian remained close enough to stay in regular contact. Maxentius' rebellion After the death of Constantius on 25 July 306, Constantine assumed the title of Augustus. This displeased Galerius, who instead offered Constantine the title of Caesar, which Constantine accepted. The title of Augustus then went to Severus. Maxentius was jealous of Constantine's power, and on 28 October 306, he persuaded a cohort of imperial guardsmen to declare him Augustus. Uncomfortable with sole leadership, Maxentius sent a set of imperial robes to Maximian and