The Council of Sardica was called as an Ecumenical Council in 342, 343, or 347 in response to the Arian Heresy. Co-Augusii Constans and Constantius, the 2 remaining sons of Constantine worked together at the urging of Pope Julius in response to this heresy that not only divided the church, but the state as well. Constans, Augustus in Rome, favored the Nicene bishops while Constantius, Augustus in Constantinople, often supported Arian ones. To help insure equal representation to solve this divisive issue, Sardica (now Sofia in Bulgaria) was chosen as a location near the division between eastern and western portions of the Roman State. However, fearing domination of the council by Western bishops, many Eastern bishops left the council to hold another council in Philippopolis. As a result, the Council of Sardica failed to universally represent the church and is not one of the official Ecumenical Councils.
Sardica produced 21 canon. In addition to the attempt to resolve the Arian issue, other major points were:
Bishops should not attempt to recruit from diocese other than their own
Bishops should be permanent residents of their own diocese
Bishops should spend most of their time in their own diocese (not at the court in Rome)
Bishops should not be transferred to another diocese
Later usage has restricted the term plenary to those councils which are presided over by a delegate of the Apostolic See, who has received special power for that purpose, and which are attended by all the metropolitans and bishops of some commonwealth, empire, or kingdom, or by their duly accredited representatives.
Synods of a somewhat similar nature (though approaching nearer to the idea of a general council) were the Council of Arles in Gaul in 314 (at which were present the Bishops of London, York, and Caerleon), and the Council of Sardica in 343 (whose canons were frequently cited as Nicene canons).
Thus, the Councils of Milevis and Carthage condemned Pelagianism, and the Council of Orange (Arausicanum) Semipelagianism.