How did Constantine help spread Christianity?

Contantine I ended the last remnants of the Great (an last) Persecution of the Christians which had started in 303. He promoted Christians to high offices in the imperial administration and arbitrated disputes between various Christian theologies. He built Christian churches, most notably, the original Basilica of St Peter's in Rome, the St John Lateran's Basilica (the city of Rome's first Cathedral and the original residence of the Popes), the Church of the Holy Apostles in Constantinople and Church of the Holy Sepulchre, in Jerusalem.