The Golden Legend, in its usual pedagogical way, gives four “reasons for the institution of this solemnity”. Last year on this day I posted the first of them; this year I give the second:
A second reason for the institution of today’s feast is one that is taken from the Itinerarium of Saint Clement. There we read that Peter was going about, preaching the Gospel, and when he approached Antioch, all the people of that city came barefoot, clothed in sackcloth, and sprinkling ashes on their heads, to meet him. They did this by way of penance, because they had taken sides against him with Simon the Magician. Seeing their repentance, Peter thanked God. Then they brought to him all the people who were sickly or were possessed by demons. Peter had them laid out in front of him and called down God’s blessing upon them, and an immense light appeared and all were cured, whereupon they ran after Peter and kissed his footprints. Within a week over ten thousand men were baptized. Theophilus, governor of the city, had his house consecrated as a basilica, in which he erected an elevated chair for Peter so that he might be seen and heard by all. Nor does this account contradict what has been said above [last year]. It is quite possible that after Peter, due to Paul’s intervention, was magnificently welcomed by Theophilus and the townspeople, he may have left the city. Then Simon Magus may have perverted the people and stirred them up against the apostle, but later they would have done penance and again given Peter an honorable reception.
– Jacobus de Voragine, Legenda Aurea
(trans. William Granger Ryan)