The Ruthenian Calendar or Hellenic Calendar also know as the "Era of the World" ( Ἔτη Γενέσεως Κόσμου κατὰ Ῥωμαίους, also Ἔτος Κτίσεως Κόσμου or Ἔτος Κόσμου) is the calendar used by the Ecumenical Patriarchate and some citizens in the Empire of Ruthenia.