letters of the name Christ as written in Greek, a device which first appeared after the time of Constantine the Great (d. 337 a.D.). This
monogram usually assumed the following form: P, and the "Monogrammatic
Cross" was made by changing the position of the Greek X (chi), and
making one of its arms serve as the straight gtroke of the Ρ (r), thus
giving the following form: P.
20 Hoernes, Urgeschichte der bildonden Kunst," Vienna, 1898, p. 338,