Within a decade of the Great Persecution the position reversed. Constantine took the west in 312 and issued with Licinius the settlement of 313 that granted free exercise to Christians and restored their confiscated property, and he then began funding basilicas, exempting clergy from public burdens and, in 325, summoning the bishops to Nicaea to settle a doctrinal quarrel he did not understand but could not allow to divide his empire. H. A. Drake has argued that Constantine's aim was a broad consensus rather than the suppression of paganism, and that the intolerance which followed was driven by bishops more than by the throne.
The direction was not settled at once. Julian, emperor from 361 to 363, attempted a restoration of the old cults with a reorganised pagan priesthood modelled on the church he had abandoned, and died before it could take hold. In 380 Theodosius I and his colleagues issued the edict at Thessalonica requiring all peoples to hold the faith of Nicaea, and in 391 and 392 he prohibited sacrifice and closed the temples.
Ramsay MacMullen's study of how the empire actually became Christian warns against reading these laws as a description of what happened: conversion was slow, uneven and driven far more by miracle, patronage and pressure from below than by imperial decree. When the western emperors ended in 476 the church was the one imperial institution still standing, holding the shape of the provinces it had grown inside.