 In the following years , Constantine gradually consolidated his military superiority over his rivals in the crumbling Tetrarchy . In 313 , he met Licinius in Milan to secure their alliance by the marriage of Licinius and Constantine 's half @-@ sister Constantia . During this meeting , the emperors agreed on the so @-@ called Edict of Milan , officially granting full tolerance to Christianity and all religions in the Empire . The document had special benefits for Christians , legalizing their religion and granting them restoration for all property seized during Diocletian 's persecution . It repudiates past methods of religious coercion and used only general terms to refer to the divine sphere — " Divinity " and " Supreme Divinity " , summa <unk> . The conference was cut short , however , when news reached Licinius that his rival Maximin had crossed the Bosporus and invaded European territory . Licinius departed and eventually defeated Maximin , gaining control over the entire eastern half of the Roman Empire . Relations between the two remaining emperors deteriorated , as Constantine suffered an assassination attempt at the hands of a character that Licinius wanted elevated to the rank of Caesar ; Licinius , for his part had Constantine 's statues in Emona destroyed . In either 314 or 316 the two Augusti fought against one another at the Battle of Cibalae , with Constantine being victorious . They clashed again at the Battle of <unk> in 317 , and agreed to a settlement in which Constantine 's sons Crispus and Constantine II , and Licinius ' son <unk> were made caesars . After this arrangement , Constantine ruled the dioceses of Pannonia and Macedonia and took residence at Sirmium , whence he could wage war on the Goths and Sarmatians in 322 , and on the Goths in 323 . 
