VIII. The Sicilian bishops are to send three of their number to each of the half-yearly meetings of bishops at Rome.
Wherefore we require this first and foremost for the keeping of perfect harmony, that, according to the wholesome rule of the holy Fathers that there should be two meetings of bishops every year, three of you should appear without fail each time, on the 29th of September, to join in the council of the brethren: for thus, by the aid of God's grace, we shall the easier guard against the rise of offenses and errors in Christ's Church: and this council must always meet and deliberate in the presence of the blessed Apostle Peter, that all his constitutions and canonical decrees may remain inviolate with all the Lord's priests.
These matters, upon which we thought it necessary to instruct you by the inspiration of the Lord, we wish brought to your knowledge by our brothers and fellow bishops, Bacillus and Paschasinus. May we learn by their report that the institutions of the Apostolic See are reverently observed by you. Dated 21 Oct., in the consulship of the illustrious Alipius and Ardaburis (447).
Source: Letters (New Advent)