This feast, attested as early as the 4th century Rome, has its roots in the ancient custom of commemorating dead relatives during the period of February 13-22 (parentalia). As a part of this commemoration, the deceased relative would have a chair set up for him (cathedra). Since the actual day of Peter’s death was unknown, his commemoration was celebrated on February 22. Eventually, the cathedra was related to his teaching office and his taking pastoral responsibility of the Church of Rome.
A similar feast used to be celebrated on January 18 in Gallia and it was adopted in Rome around the year 600. Trying to give more content and meaning to these two feasts, February 22 was celebrated as Peter’s taking pastoral responsibility of the Church of Antioch, whereas January 18 was associated with Rome. Both feast days were prescribed for the whole Church in 1558. The more recent reform of the liturgical calendar gave up January 18 and focused on February 22.
The mass formular and prayers talk about the task and activity of the apostle Peter. The feast commemorates the office of supreme pastor conferred by Christ upon St. Peter and continued in unbroken succession to the present. It celebrates the unity of the Church, which is founded upon the Apostle, and reinforces assent to the teaching office of the Roman Pontiff, extending both to truths solemnly defined ex cathedra and to all acts of the ordinary Magisterium.
Another old feast associated with Peter, The Chains of Peter (August 1) is not celebrated any more.
Visitors of Saint Peter’s Basilica in Rome also have a unique opportunity to see the bronze statue of St. Peter dressed in Papal vestments on this day.