On the tombs of the early Christians, in the Roman catacombs, these letters (ΙΗΣ) were sometimes found (though not so frequently as the next monogram). They are, in the Greek character, the first three letters of the sacred name of Jesus— ΙΗΣΟΥΣ. The third letter, sigma, had in early Greek two forms, C and Σ; hence the apparent variety in what is really one and the same Monogram.
The second Monogram, now rarely seen, but formerly much employed in memorial inscriptions, is called the Cross of Constantine. It consists of the two Greek characters, Χ and Ρ. Χ stands for, or is equivalent to, our CH; Ρ, the Greek rho, is translated by our letter R: thus we have the equivalent of the first three letters of the sacred name of Christ—in Greek, ΧΡΙΣΤΟΣ.
It is related, on the authority of Eusebius, that the Emperor Constantine, while engaged in prayer, suddenly saw this sign in the sky, and that it was also visible to his whole army; over the sign was an inscription signifying "Conquer by this," or, "In this sign thou shalt conquer" (In hoc signo vinces). On the same night the Emperor had a dream—a vision of the Saviour appearing to him with the same sign, commanding him thenceforth to bear it on his banner, whereby he should always be victorious. In obedience to this revelation, the Emperor immediately caused such a banner to be constructed, and afterwards wore the sacred sign upon his helmet. This banner was called a labarum, of which we find the following brief account in Fosbrooke's Encyclopædia of Antiquities:—
"The name, but not the thing, commences with Constantine. It is a standard, with a cross-piece, from which hung a piece of stuff. The Romans borrowed it from the Germans, Dacians, &c.; and upon coins of Augustus, and the emperors preceding Constantine, it refers to some conquered nation. It had an eagle painted or embroidered, till Constantine, who added the cross, monogram of Jesus Christ, and Α and Ω" (Alpha and Omega: see Rev. i. 8). "Sometimes, above the flag, was a crown, in the midst of which was the monogram mentioned. From the cross-piece hung a square stuff, upon which Constantine placed the figures of himself and his children in gold."
The above is an original example of the two Monograms combined, well suited for illumination.
The following is a beautiful illustration, in a simple form, of the doctrine of the Holy Trinity in Unity:—
Read thus:[21] "Pater non est Filius. Filius non est Sanctus Spiritus. Sanctus Spiritus non est Pater. Pater est Deus. Filius est Deus. Sanctus Spiritus est Deus."