 Maxentius ' rule was nevertheless insecure . His early support dissolved in the wake of heightened tax rates and depressed trade ; riots broke out in Rome and Carthage ; and Domitius Alexander was able to briefly usurp his authority in Africa . By 312 AD , he was a man barely tolerated , not one actively supported , even among Christian Italians . In the summer of 311 AD , Maxentius mobilized against Constantine while Licinius was occupied with affairs in the East . He declared war on Constantine , vowing to avenge his father 's " murder " . To prevent Maxentius from forming an alliance against him with Licinius , Constantine forged his own alliance with Licinius over the winter of 311 – 312 AD , and offered him his sister Constantia in marriage . Maximin considered Constantine 's arrangement with Licinius an affront to his authority . In response , he sent ambassadors to Rome , offering political recognition to Maxentius in exchange for a military support . Maxentius accepted . According to Eusebius , inter @-@ regional travel became impossible , and there was military buildup everywhere . There was " not a place where people were not expecting the onset of hostilities every day " . 
