Galerius refused to recognize Maxentius as emperor and sent Severus II to crush him. Gathering a number of legions in Mediolanum, Severus invaded Italy, but was undone when most of his army deserted him. Fleeing north, Severus took refuge in Ravenna, only to be tricked into surrendering to Maxentius and imprisoned.
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While Maximian was in Gaul negotiating with Constantine, Galerius launched an invasion of Italy and advanced to the gates of Rome, prompting a panicked Maxentius to execute the captive Valerius Severus. However, the immense size of the city apparently astounded Galerius, who had never visited it before, and he soon realized he lacked the forces to capture it. With winter approaching, his troops low on morale, and the population hostile, the emperor was forced to withdraw from the peninsula and admit defeat.
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In a public gathering in Rome in April 308, Maximian, angered by the execution of Severus, blamed his son Maxentius for the troubles they faced and attempted to relieve him of the rank of Augustus. The crowd and the army immediately sided with Maxentius, forcing Maximian to flee to Gaul and the court of his son-in-law Constantine.
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Following the exile of Maximian, Maxentius sent his own image to Carthage to demonstrate that he was now sole Augustus, but was rebuffed by the African legions, who had great respect for Maximian. When an angered Maxentius tried further measures to assert his authority in the region, the African legions revolted and proclaimed their vicarius Domitius Alexander as Augustus. Alexander—an elderly man who may have earlier served as Maximian’s praetorian prefect—quickly gained support across Africa and as far as Sardinia.
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