This article examines the circumstances associated with several sessions held in Rome in December 531 considering the case of Stephanus, Metropolitan of Larissa in Thessaly. In the presence of Pope Boniface II (530–532), the representative of Stephanus Theodore, bishop of the city of Echinus, read out the complaints sent by Stephanus and his associates to the pontiff against the actions of the Patriarch of Constantinople, by whose judgment Stephanus had been deposed. The letters of Stephanus and his colleagues were enclosed with the acts, which, together with the letters of the popes directed to the bishops of Illyricum between the 4th and 5th centuries attached to them, made up a collection known as the Collectio Thessalonicensis. The purpose of this article is to study the acts of the aforementioned sessions in order to clarify their ecclesiastical status, to investigate the circumstances and canonical foundations of the case of Stephanus of Larissa, as well as the role of the Patriarch of Constantinople both in the case of the Metropolitan of Larissa and in Illyricum as a whole during the period. The author concludes that the sessions of December 531 in the papal curia were not a council, despite the fact that in the secondary literature they are called exclusively that way. It is further concluded that the case against Stephanus of Larissa is a classic case against a Metropolitan, regulated by canons 9 and 17 of the Council of Chalcedon, according to which the Archbishop of Constantinople should consider such a case, as well as by the imperial legislation. Since the legal sentence of the prelate of the capital against the Thessalian metropolitan was final, Stephanus’ appeal to Rome was uncanonical and had no legal consequences.