Great Union Day (Romanian: Ziua Marii Uniri; also called Unification Day or National Day) is a Romanian national holiday celebrated on 1 December to mark the 1918 Great Union (the unification of Transylvania, Bassarabia, and Bukovina with the Romanian Kingdom). The holiday was declared after the Romanian revolution and commemorates the Great National Assembly of the delegates of ethnic Romanians held in Alba Iulia, who declared the Union of Transylvania with Romania.
Until the abolition of the Romanian monarchy in 1947, the national holiday was observed on 10 May, which had a double meaning as it was the date on which the future King Carol I first set foot on Romanian soil in 1866 and on which he later ratified Romania's Declaration of Independence from the Ottoman Empire in 1877. During the communist regime from 1947 to 1989, the national holiday was observed on 23 August (Liberation from Fascist Occupation Day) to mark the 1944 overthrow of Ion Antonescu's government by King Michael I, with parades held in Charles de Gaulle Square (then called Stalin Square and later Aviators' Square). In 1990, the holiday's date was moved to 1 December to match the date of the Great Union.