Arianism would not be contained within the Alexandrian diocese. By the time Bishop Alexander finally acted against his recalcitrant presbyter, Arius's doctrine had spread far beyond his own see; it had become a topic of discussion—and disturbance—for the entire Church. The Church was now a powerful force in the Roman world, with Constantine I having legalized it in 313 through the Edict of Milan. The emperor had taken a personal interest in several ecumenical issues, including the Donatist controversy in 316, and he wanted to bring an end to the Arian dispute. To this end, the emperor sent bishop Hosius of Corduba to investigate and, if possible, resolve the controversy. Hosius was armed with an open letter from the Emperor: ""Wherefore let each one of you, showing consideration for the other, listen to the impartial exhortation of your fellow-servant."" As the debate continued to rage despite Hosius' efforts, Constantine in AD 325 took an unprecedented step: he called an ecumenical council composed of church prelates from all parts of the empire to resolve this issue, possibly at Hosius' recommendation.