Pope Xystus (Latinized as Sixtus) reigned over the Catholic Church from AD 117 to 126 during the reign of Adrian “a conulatu Nigri et Aproniani usque Vero III et Ambibulo.”

The Liber Pontificalis credits Pope Sixtus with two liturgical developments. First, Pope Sixtus stipulated that only deacons, priests, and bishops were allowed to touch the sacred vessels (e.g. paten and chalice). Touching these vessels even outside of Holy Mass was forbidden to the laity. 

Secondly, Pope Sixtus decreed that the threefold Sanctus should be chanted in the Holy Sacrifice of the Mass.* Apparently, this practice was common in the East, but not yet universal in the West.

Sixtus also decreed that bishops who have been summoned to Rome shall, upon their return, not be received by their diocese except on presenting Apostolic letters from the Pope. This reveals that as early as AD 126, the Catholic Church had recognized that the Pope of Rome could depose bishops.

* The Sanctus of the Holy Mass derives from Isaiah 6:3 and Apocalypse 4:8: