What made constintine convert to Christianity?

Answer 1

Constantine supported and instituted Christianity as the main religion of the Byzantine Empire in order to gain support and political power in return. It is possible he believed that the Christian God was real, but did not convert to Christianity officially until he was baptised, practically on his deathbed. Constantine lived in a culture that would have accepted the concept of an afterlife and presumably sought to secure his afterlife in any way possible.

Answer 2

He had a vision the night before his battle that told him if he carried the cross he would win.