It might be better if you defined "liberal" a little bit because a modern term that has many aspects to it is hard to apply. Is religious toleration the most important aspect? Then yes you could say Konstantine was tolerate, but there were countless individuals that did the same thing like King Cyrus of the Persian empire because Zoroastrian philosophy preaches toleration to an extent.

Anyway maybe you should change your research topic and questions from something more complex like "liberal" to something more simple like toleration and then work your way from there.