Ascending to the papal throne in the year 432, Sixtus III in a decisive way took over the role of founder of sacral structures, which until then had been the domain of the emperor and his family or wealthy donors. He also, commissioned one of the grandest churches in Rome – the Santa Maria Maggiore, in which both Romans as well as pilgrims could experience the might of the pope and the apostolic city. The church was a kind of a result of the Council of Ephesus (431), where the dogma on the Divine Motherhood of the Blessed Virgin was announced, in this way introducing a new feast to the calendar (Our Lady of the Snows) and a new saint – Mary, the Mother of God. The church was decorated with magnificent mosaics, furnished with gold and silver liturgical paraments and silver altars. Jerome (the latter saint) deplored over these gilded walls and altars shining with precious stones, however, his voice was inaudible, or on the rare occasions when it was heard, it was treated with protective aloofness – the time of modesty, in-house gatherings of the faithful and celebrations concentrated on the Word of God had passed. Both the rich and the poor willingly spent time in exquisite churches, while pompousness only added splendor and strengthened the faith which had already been made into a state religion and was fully victorious over the still recently tolerated pagan cults. The form itself of the newly erected basilica – with a row of Ionian columns and classic in style mosaics – is however an evidence of adapting ancient patterns and is a continuation of Roman art of the IV century.

After the pagan temples had been shut down, while pagan cults forbidden, the identification of the papacy with centuries-old Rome only took place not only in the spirit of ancient achievements – as far as law, philosophy or architecture, but also through a sort of ideological parallel. As Jupiter had watched over Rome previously, now it was watched over by a Christian God and two apostles, Peter and Paul, who – as Romulus and Remus – became patrons of the city. A new Rome was born, not an imperial one but a papal one instead.

The important from the prestigious point of view Basilica of St. John on the Lateran (San Giovanni in Laterano), found next to the pope’s residence and thus treated with equal respect to St. Peter’s Basilica (San Pietro in Vaticano), was decorated with similar enthusiasm.

Sixtus III was only bishop of Rome for eight years, while this period was marked with frequent at that time doctrinal disputes of various branches of Christianity – mainly Pelagians and Nestorians.

A trial over the rape of a nun brought infamy upon the pope’s name, but since the accusers were unable to find witnesses of this event, the dignitary was freed from all accusations.

In the Liber Pontificalis there is an unclear note about the Church of St. Lawrence Outside the Walls (San Lorenzo fuori le mura), which was allegedly also founded by Sixtus III, although most likely this was only a building which belonged to that complex. It was probably in this very building that the pope’s earthly remains were laid to rest after his death.

Other structures created at the initiative of Sixtus III or during his pontificate:

•     Basilica of Santa Maria Maggiore – mosaics still visible today in the part of the triumphal arch (scenes of the birth and adolescence of Christ) in the part under the windows of the main nave (scenes from the Old Testament). The architrave was also preserved along with the twenty columns supporting it on each side of the main nave. In the apse there were mosaics depicting Our Lady surrounded by saints (later replaced with other mosaics). The dedicative inscription seen on the triumphal arch of the church proclaims: Xystus episcopus plebi Dei, which means “Bishop Sixtus for the God’s people”.
•     Providing a new architectural look for the San Giovanni in Laterano Baptistery and decorating it with mosaics and marble decorations (only preserved in part of the vestibule)
•     Enriching the complex of the Church of San Sebastiano at via Appia Antica with a new monastery
•   Erecting the Church of San Pietro in Vincoli (its founder was Empress Licinia Eudoxia)
•     Erecting the Church of San Lorenzo in Lucina
•   Completing the construction of the Basilica of Santa Sabina, started by the previous pope, Celestine I.