Eusebius, Ecclesiastical History. IV, 4. "In the third year of the same reign [Hadrian], Alexander, bishop of Rome, died after holding office ten years. His successor was Xystus". IV, 5. "In the twelfth year of the reign of Adrian, Xystus, having completed the tenth year of his episcopate, was succeeded by Telesphorus, the seventh in succession from the apostles." The Caesarean calendar bean in 3 October, see Burgess, Richard W. (1999). Studies in Eusebian and Post-Eusebian Chronography. Franz Steiner Verlag. p. 29. ISBN978-3-515-07530-5.
Eusebius, Ecclesiastical History. IV, 4. "In the third year of the same reign [Hadrian], Alexander, bishop of Rome, died after holding office ten years. His successor was Xystus". IV, 5. "In the twelfth year of the reign of Adrian, Xystus, having completed the tenth year of his episcopate, was succeeded by Telesphorus, the seventh in succession from the apostles." The Caesarean calendar bean in 3 October, see Burgess, Richard W. (1999). Studies in Eusebian and Post-Eusebian Chronography. Franz Steiner Verlag. p. 29. ISBN978-3-515-07530-5.
newadvent.org
"Pope St. Sixtus I". The Catholic Encyclopedia. Vol. 14. New York: Robert Appleton Company. 1912.
tertullian.org
Jerome, Chronicon, 3rd year of Hadrian, AD 119. "Xystus holds the 6th episcopate of the Roman church for 10 years." AD 128, 12th year of Hadrian: "Telesphorus received the seventh episcopate of the Roman church for 11 years."
