Indeed. He donated several basilicae to the Church to use for worship and personally gave the Church land and finances to build a new basilica as a monument to St. Peter.
And the first ecumenical council at Nicea?
Hosius Cordubensis, a Spanish bishop, proposed the idea - due to the fact that the Arians were gaining ground in Spain.
After consulting with the bishops (who had already held a number of local synods regarding these matters), Constantine offered both a venue and safe passage to to Nicaea for all the bishops able to make the journey. Such a gathering was never possible before - the last time such a Council had been held was in Jerusalem during the time of the Apostles.
Constantine attended, but did not interfere and seated the bishops before he sat down - a breach of royal protocol to demonstrate that he was not in charge: the bishops were.