Adoption of the Gregorian calendar for secular use occurred in Eastern Orthodox countries as late as the 20th century and some religious groups in some of these countries still use the "old style" (O.S.) Julian calendar for ecclesiastical purposes. The Kingdom of Bulgaria changed from the Julian to the Gregorian calendar during the First World War on 31 March 1916, where the next day was 14 April 1916. The Ottoman Empire's Rumi calendar, used for fiscal purposes, was realigned from a Julian to a Gregorian starting on 16 February/ 1 March 1917. The beginning of the year was reset to 1 January starting in 1918.
Arabic names of calendar months are regional variations of the Berber calendar, since some communities did not recognise the Julian 29 February in century years where the Gregorian calendar had no equivalent date. When Morocco adopted the Gregorian calendar for civil purposes, the names of the months were taken from this local tradition. Arabic names of calendar months The Arabic names of calendar months of the Gregorian calendar are usually phonetic Arabic pronunciations of the corresponding month names used in European languages. An exception is the Assyrian calendar used in Iraq and the Levant, which is inherited from Classical Arabic that correspond to roughly the