Barely visible in the center of this weathered gravestone cross are the letters “ihs”, a common Christian abbreviation for the name of Jesus. It derives from the first three letters (iota-eta-sigma) of Jesus in Greek: ιησούς. Used as a Christian symbol, it’s just one example of what is called a Christogram. Here is a much more stylized celtic-knot ihs variant taken in the same cemetery as the above image.

One of the oldest Christograms is the labarum — the first two letters (chi-rho) of Christ in Greek: χριστός. It is often found inscribed with an added alpha (α) and omega (ω) — the first and last letters of the Greek alphabet — in order to reference Revelation 22:13 in the New Testament.

Francesco Carotta believes that the labarum derives from the sidus Iulium (on the right; a second example is here, on the left), a 44 BC comet that was sold as a manifestation of the soul of Julius Caesar ascended into heaven. Suetonius writes that “this is why a star is set upon the crown of his head in his statue.”

Not an awful lot is known about Divus Julius, the cult that venerated Caesar. Augustus, Caesar’s great-nephew and adopted son, used his status as Divi filius to further his own political aspirations. After his death in 14 AD, Augustus was also decreed a god. Mention of Divus Julius ceases with the Christianization of the Empire in 391 AD.