Pope Gregory XIII introduced the Gregorian Calendar in a papal bull dated 24 February 1582. A few countries adopted it and others followed over the next few centuries. Adoption was slowed because of Reformation politics; Greece was the last European country to adopt it, with March 1, 1923 following February 15, 1923. Other calendars (e.g., Arabic and Judaic) are still in use, generally for religious reasons.