During the early years of his reign constantine had campaigned in Gaul and Britain and resided primarily in Trier. In 310, in the emperor's presence at Trier, an orator celebrated the successful outcome of his recent confrontation with Maximian, one of the original Tetrarchs. Despite his abdication in 305, Maximian had returned to imperial rule to help his son, Maxentius, who had become an emperor at Rome in 306. That assistance had included an alliance with Constantine, who was himself looking for support. Because he had been proclaimed as an emperor by his father's troops in Britain, his accession had defied the wishes of Galerius, the current dominant senior emperor in the Tetrarchy. Even after Galerius had begrudgingly recognized him as a Caesar, a junior emperor, in the Tetrarchy, Constantine's position was still shaky. In 307 he married a daughter of Maximian, who then sanctioned his new son-in-law's rank as an Augustus, a senior emperor.

This alliance with the dissident dynasty of Maximian and Maxentius soon became a liability, however. After a confrontation with his son at Rome, Maximian fled to his son-in-law in Gaul. But at a summit meeting in 308 Maximian had to retire again as emperor, and Galerius again accepted Constantine as a Caesar. In 310 Maximian challenged his host son-in-law and tried to buy the loyalty of troops in southern Gaul. Although Constantine soon suppressed this uprising at Marseille, the threat remained until Maximian's shameful death.