What is the X in X-mas?
1660s, from Greek akropolis "citadel" (especially that of Athens), from akros "highest, upper" (see acrid) + polis "city" (see polis).
The fortified high point of ancient Athens. Once the center of Athenian life, the Acropolis is now the site of famous ruins, including the Parthenon. In Greek, the word means “high” (acro) “city” (polis).