Pope Sixtus III (Pope from 432–440 AD) is remembered as a pious administrator, defender of orthodoxy, peacemaker in doctrinal disputes, and patron of Roman Christian architecture. When you visit Rome, some of the primary places you will probably want to see are due to his efforts. He is notably associated with a building boom in Rome in the decades after the Visigothic sack of 410 AD, a period that some scholars call a "Sixtine Renaissance" in early Christian Roman architecture and art.
Key projects included restoring and enlarging the Basilica of Liberius, transforming it into the grand Basilica of Saint Mary Major (Santa Maria Maggiore). This dedication to Mary directly reflected support for the Ephesus council's teachings that declared Mary to be Theotokos ("God-bearer" or "Mother of God") and condemned Nestorianism, which taught that she only bore the human nature of Christ. The nave mosaics from his era (c. 432–440) survive and depict biblical scenes.
Pope Sixtus III died of natural causes on August 18, 440 AD (some sources say August 19). The mortal remains of Saint Sixtus III are buried in the Basilica of Saint Lawrence Outside the Walls (San Lorenzo fuori le mura) in Rome which, as mentioned above, was one of his rebuilding projects.. While his burial at the Basilica of Saint Lawrence is well-documented by historical authorities such as the Liber Pontificalis, the exact location of his tomb within the church is currently unknown.
Some older traditions occasionally confused him with Sixtus I (buried near St. Peter) or Sixtus II (buried in the Catacombs of St. Callixtus), but modern scholarship confirms his resting place is at Saint Lawrence.