See Edward C. Whitaker, Documents of the Baptismal Liturgy (London: Society for Promoting Christian Knowledge, 1970); Willy Rordorf, Sunday: The History of the Day of Rest and Worship in the Christian Church (Philadelphia: Westminster, 1968); Jacob Vellian, ed., Studies on Syrian Baptismal Rites, Syrian Church Series 6 (Kottayam, India: C.M.S. Press, 1973); Josef A. Jungmann, The Early Liturgy: To the Time of Gregory the Great (Notre Dame, IN: University of Notre Dame Press, 1959).