Excerpts from Books and Wikipedia
" . . . they granted all people freedom to worship whatever deity they pleased. . . . The so-called Edict of Milan did not make Christianity the official religion of the Roman Empire--that would not happen until Theodosius I outlawed pagan worship and closed all the pagan temples in 391 . . . Yet it was only on his deathbed in 337 that he [Constantine] took the final step of receiving Christian baptism." [1001 Days]
"The two men met in Mediolanum (modern Milan) to celebrate Licinius’s marriage to Constantia and to issue an empire-wide proclamation that made Christianity legal, which was highly necessary given that both men had now wrapped themselves in the flag of God in order to claim the right to rule. . . . Christianity was the empire's best chance for survival." [Bauer: Medieval World, p. 6]