What is it about?
Church historians affirm positively that St. Peter founded the See of Antioch before he went to Rome. Antioch was then the capital of the East.
St. Gregory the Great states that the Prince of the Apostles was Bishop of that city for seven years. It is also a fact, based upon the unanimous consent of Christian antiquity, that St. Peter was at Rome and founded the Church there. However, his sojourn in the capital of the Roman Empire was not continuous, as he was often absent when performing his apostolic functions in other countries.
This feast, which commemorates St. Peterīs pontifical authority, formerly was celebrated on two different days: on January 18, in honor of his pontificate at Rome, and on February 22, in honor of his pontificate at Antioch.
Reference: Lives of the Saints - Catholic Book Publishing Co.- Nihil Obstat: Daniel V. Flynn, J.C.D. - Imprimatur: James P. Mahoney, D.D., Vicar Gen., Archdiocese N.Y. - Copyright 1955-1974-1977