The pilgrimage is organized each year by seminarians and priests of the Pontifical North American College in Rome. An early morning (7 a.m.) Mass is celebrated in English at one of these churches each day (except Sunday) throughout Lent. It is a practice which goes back to the early Church when the pope, as bishop of Rome, would pay a pastoral visit to the parishes of the city.
One of the oldest churches in Rome, Santa Maria in Trastevere was built on the site where, according to legend, oil miraculously sprung forth from the ground on the day Mary the mother of Jesus was born. Built in the 4th century, the church to this day enjoys an active parish life, and is closely tied to the San'Egidio Community – a movement known for its work with the poor. The parish also hosts a Byzantine Liturgy with roots in Italy, celebrated each Sunday evening in the Italian language.
J. Stanton Good, who works as a professional tour guide in Rome, explained to ZENIT that Santa Maria in Trastevere was likely the center of the early Church. Translated "across the Tiber," the region of Rome known as Trastevere hosted an international community during the Roman empire as it was located close to a port. Good said there is proof of Christian worship at the site of the church going back to the 4th century, although there is "the possibility of Christian worship in the vicinity even before that when Christianity was still illegal."
"There are three ancient churches in Trastevere, what we would call 'Paleo-Christian' churches," he said. "The very oldest churches going back to the 5th and 4th century when the Roman empire was still standing. This is the most characteristic of the three."
Speaking on the legend surrounding the site, Good noted how it was significant that the miraculous oil erupted in a pagan neighborhood of Rome on the day the Virgin Mary was born in the East. "This is an interesting tradition," he said. "For instance, people go into the Sistine Chapel and wonder why there are five Greek pagan symbols on the ceiling of a Christian place. A natural phenomena happening, it seems, at the same time the Virgin Mary is born. After Christianity is legalized and becomes the majority religion – then becoming the only religion – we look back in time and we start to rehash all of these old pagan prophesies."
Santa Maria in Trastevere was also the site of key ecclesiastical moments in the Church's history, Good said, explaining that a conclave was held in the church. "When the popes came back from Avignon in 1378 Saint John Lateran had been burnt to the ground twice in 55 years. They came here because this church was still standing. You had some very important ecclesiastics in this church."
Artistically, the church is rich in Marian imagery, much of which is stylistically Byzantine. The façade of the building presents a 12th century mosaic of Mary, flanked by angels, breastfeeding the Christ child as she sits on a throne. Inside the Church, in the apse above the altar, a domed 13th century mosaic made of glass also represents Mary on a throne, this time beside an adult Jesus who has His arm around His mother. Flanking the altar are panels which depict the life of Mary, again in the style of Byzantine mosaic, beginning with her life and ending with her dormition. Contained in the "Altemps chapel," located just left of the main apse, is one of the oldest images of Mary in the world. The image is historically significant in that it dates to the iconoclast controversy, which stated that sacred images of our Lord and the saints were not to be used. The controversy drove many icon painters to Rome, bringing this form of religious art to the city, Good explained.
Good concludes: "Santa Maria in Trastevere is, in my experience, the most active of the ancient Churches – the best combination of antiquity and an active Church for living worship."