"At Rome, the Greater Litanies at St. Peter's."
I thought some of our readers, particularly those with an interest in the history and tradition of the Roman church, would be interested to read a little bit about what Cardinal Schuster had to say about these processions.
From the second volume of his work, The Sacramentary:
This intercessory rite is called the "Greater Litanies" because it was of a much more solemn nature than the ordinary stational litanies. The route was very long, and there took part in the procession the whole population of Rome, divided into various companies. The rite must already have been fully established at the time of St. Gregory...
As this procession and the stational Mass at St. Peter's always occured at Eastertide, they had a distinctly festal character, in which they differed from the processional litanies which took place during Lent, these being especially distinguished by their penitential nature.
The Pope having recited the Collect, a subdeacon took from the altar the stational cross, and presented it to be kissed by all present, after which the procession set forth towards Sta Maria Nova in the Forum, where the first halt was made. When the Pontiff was somewhat rested, they proceeded to St. Mark's, where there was another pause. They next went towards the Mausoleum of Hadrian, the third halting-place, and finally in the direction of the Vatican.
Both Schuster and Jungmann (see The Early Liturgy to the Time of Gregory the Great p. 145) speak to the pre-Christian origins of this procession, rooted in ancient Rome and then later modified to serve Christian purposes.