The position of the Roman see at this period in the Western Church is often wrongly represented, or vaguely understood. At the end of the fourth century the bishops of Rome, beyond their acknowledged primacy in Christendom, possessed at least two important rights which secured them a large influence in the ecclesiastical affairs of the western provinces of the Empire.[50] The Roman see was recognised by imperial decrees of Valentinian I. and Gratian as a court to which clergy might appeal from the decisions of provincial councils in any part of the western portion of the Empire. Of not less practical importance was another distinctive prerogative, which, though not recognised by any formal enactment, was admitted and acted upon by the churches of the west. The Roman Church was regarded as the model church, and when doubtful points of discipline arose, the bishops of the Gallic or other provinces used to consult the Bishop of Rome for guidance, not as to a particular case, but as to a general principle. The answers of the Roman bishops to such questions are what are called _decretals_. No decretals are preserved older than those of Damasus,[51] and perhaps it was in his pontificate that the practice of such applications for advice became general. The motive of the custom is evident. It was to preserve uniformity of discipline throughout the Church and prevent the upgrowth of divergent practices. But those who consulted the Roman pontiff were not in any way bound to accept his ruling. The decretal was an answer to a question; it was not a command. Those who accepted it were merely imitating the Roman see; they were not obeying it. The appellate jurisdiction, and the decretals which were gradually to be converted from letters of advice into letters of command, were the chief foundations on which the spiritual empire of Rome grew up. But in the latter part of the fourth century its nascent authority was confronted by a serious danger in the shape of a rival. When Milan instead of Rome became the imperial residence in Italy, the see of Milan assumed immediately a new importance and prestige. Its bishop soon came to be regarded as an authority to which appeals might be addressed, as well as to the Bishop of Rome. This new dignity was justified by the personality of Ambrose, who then occupied the see, but it was due to the presence of the Augustus. If his presence had been lasting, it is possible that Mediolanum would have become in regard to Rome what Constantinople became, because it was the Imperial city, in regard to Alexandria and Antioch. But the danger passed away when the Emperor Honorius migrated to Ravenna, though the consequences of the transient rivalry of Milan with Rome can be traced for a few years longer.