Although Sixtus is claimed to be a pope by the writings of St. Ireneus and Eusebius, there is not good historical accuracy for that claim. Although it is known that there were bishops in Asia Minor, such as James, in Jerusalem, and Polycarp, in Smyrna, there does not seem to be any indication of the men, listed as pope in the first century after Peter, being actual heads of the whole Catholic Church. Most research shows that the Church in Rome was ruled by a group of presbyters, not an individual. The implication, then, is that there was not a bishop of Rome until the middle of the second century.
Hegesippus, a man of the Middle East who lived during the second century (d. 180 AD), was a chronicler. He traveled extensively. He appeared quite knowledgeable in Hebrew and Jewish unwritten traditions. Some years after Sixtus died, Hegesippus arrived in Rome. A Christian himself, he questioned the Roman Christians about their traditions. Knowing that bishoprics were common in the Middle East, he may have assumed that the same was common in Rome, so the names of the bishops of the city were really just popular presbyters named by those he was questioning, including Sixtus.
Not to give him less than his due, Sixtus was probably one of the presbyters, or elders, of the Church in Rome. He was born about 42 AD and was said to have governed 114/115 to 125/128 AD. He was obviously old by the time he was acknowledged as a senior member of the Church. Tradition has it that Sixtus (or Xystus, as the first three popes of that name were spelled) was of a Roman family and his father was a pastor. This implies that Sixtus was raised as a Christian.
Many developments in the liturgical and organizational aspects of the Church have been credited, probably incorrectly, to Sixtus. It is said that he ruled that the Sanctus, Sanctus, Sanctus was to be said immediately after the Preface, said by both priest and congregation. He, it is said, was the one who dictated that only those in Holy Orders could touch the sacred vessels. And, again, it is supposedly he who ruled that when a bishop was called to Rome, a letter of greeting would be written to be presented to the parishioners at home when the bishop returned, to keep the Church in communications. At this time in historical research, it cannot be proven that he did any of these.
The Emperor Hadrian, a pagan, was a philosopher and intellectual. He reduced the persecution of the Christians with this letter to one of his proconsuls in Africa: “If someone brings charges and can prove that the Christians who commit offenses against the laws are guilty, leave, then punish them for their crimes. By Hercules, yet if someone is just looking for a mere pretext to punish them, then you have to decide depending on the severity and punish them instead.”
Sixtus was not likely martyred given the peaceful nature of the Empire during Hadrian’s reign, which extended to 138 AD. No matter how much, or little, we have recorded about him, his most important contribution was helping to lead the Church in its infancy.