Most people associate the Chi-rho with Christianity, but the first time a chi-rho was used, happened in the Ptolemaic Kingdom of Egypt.
I wrote a bit about this on my webpage, but I was cataloguing the first coin below and thought it would make a good topic for those not aware.
http://www.constantinethegreatcoins.com/symbols/Ptolemaic Kingdom of Egypt, Ptolemy III Euergetes. Æ Diobol (29mm 21.0gm) Alexandria, circa 245-222 B.C.; Diademed head of Zeus-Ammon right / BAΣIΛEΩΣ ΠTOΛEMAIOY, eagle left on thunderbolt; in front cornucopiae; between legs chi-rho monogram. SNG Copenhagen 176-177.
