29. Labarum of Constantine.
Another suggestion is that the shape of the saltire cross, both of the Irish and the Scotch, is derived from the Labarum (29), or Sacred Standard, which was raised by Constantine the Great, the first Christian emperor of Rome, as the imperial standard of his armies. On this he had placed a monogram composed of the first two letters, ΧΡ (ChR), of the Greek form of the sacred name of Christ (ΧΡΙΣΤΟΣ), and the saltire cross is reputed to be the repetition of the Χ of the lower part of the Christian emblem.
The Labarum was the official standard of the Emperor of Rome, and upon it were displayed the "insignia" of the emperor of the day. Constantine, after his conversion to Christianity, had changed his previous insignia to the Christian emblem.
Should this latter suggestion of the origin of the cross of the saltire shape be accepted as the preferable one, this saltire cross has yet a most interesting and particular connection with the early history of Ireland.
The Roman Governor of Britain, under the Emperor Diocletian, when, in A.D. 301, the pacification of IBERNIA (Ireland) had been completed, was Constantius Chlorus, the father of Constantine.
30. Harp of Hibernia.
The goddess of the pagan islanders was the Goddess Hibernia, whose emblem was a harp, and this Hibernian Irish harp (30) Constantius had in testimony of his success adopted as the insignia for his standard.
After the resignation of Diocletian, Constantius Chlorus and Galerius were created joint emperors of Rome, and, dividing the empire between them, Galerius took the East and Constantius the West.