Constantine the Great zealously accepts Christianity and patronizes the faith. Yet his support for the Church is gradually seen as a threat to his own rule, as it became a parallel source of authority. So he convenes all Christian bishops to meet at Nicaea, promising to plot the course of the faith.
Yet on the way, most bishops are seized by legions before arriving, and those who do arrive at Nicaea are personally arrested by Constantine. He immediately issues a proclamation that it is heretical for the faith to be organized by mortals on earth, and that all bishops will be defrocked and forced to return to lay life. All land and property belonging to the Church is seized, officially because of their doctrinal heresy. Yet he remains a devout follower of Christ and continues to support local clergy, being careful to ensure they do not organize on a large scale.
With a lack of doctrinal dogma, the Church becomes decentralized. Most Romans are "Christian", all Roman towns have elaborate churches, yet pagan gods are widely worshiped.