When thanks to the the Byzantines (who dominated Rome from its conquest by Belisarius until the Iconoclast controversy) the cult of the martyrs Cosmas and Damian reached a great degree of celebrity in Rome, the Paschal stations had for several years already been distributed among the most distinguished basilicas of the city. As a result, no place remained for the one Pope Felix IV had dedicated to these Martyrs on the Via Sacra. A station at this basilica was therefore assigned to the second Sunday after Easter.
But this practice did not last long: on the second Sunday after Easter, the Gospel pericope about the Good Shepherd was read, and that naturally drew the faithful to think of St Peter. A sort of compromise was then reached between him and the martyrs Cosmas and Damian; on the second Sunday after Easter, the station was fixed at the Vatican Basilica, but at the same time it was decided that today in the evening the Pope should betake himself to celebrate the Vesperal station at the church of Sts Cosmas and Damian. According to the Roman ordines, the titular clergy there used to prepare a frugal meal for the Pontiff and his retinue, consisted of bread, wine, milkmeats, and lettuce.
Blessed Ildefonso Cardinal Schuster, Liber Sacramentorum, vol. IV, pp. 103-4.