 In 310 AD , a dispossessed Maximian rebelled against Constantine while Constantine was away campaigning against the Franks . Maximian had been sent south to Arles with a contingent of Constantine 's army , in preparation for any attacks by Maxentius in southern Gaul . He announced that Constantine was dead , and took up the imperial purple . In spite of a large <unk> pledge to any who would support him as emperor , most of Constantine 's army remained loyal to their emperor , and Maximian was soon compelled to leave . Constantine soon heard of the rebellion , abandoned his campaign against the Franks , and marched his army up the Rhine . At <unk> ( Chalon @-@ sur @-@ Saône ) , he moved his troops onto waiting boats to row down the slow waters of the Saône to the quicker waters of the Rhone . He disembarked at Lugdunum ( Lyon ) . Maximian fled to Massilia ( Marseille ) , a town better able to withstand a long siege than Arles . It made little difference , however , as loyal citizens opened the rear gates to Constantine . Maximian was captured and reproved for his crimes . Constantine granted some clemency , but strongly encouraged his suicide . In July 310 AD , Maximian hanged himself . 
