55 Other manifestations of piety have also played their circumstantial part in this same liturgical development. Among them may be cited the public pilgrimages to the tombs of the martyrs prompted by motives of devotion, the special periods of fasting instituted for the same reason, and lastly, in this gracious city of Rome, the penitential recitation of the litanies during the "station" processions, in which even the Sovereign Pontiff frequently joined.
Source: Mediator Dei (Vatican.va)