Terra Mariana (Land of Mary) was the official name for Medieval Livonia or Old Livonia (German: Alt-Livland, Estonian: Vana-Liivimaa, Latvian: Livonija), which was formed in the aftermath of the Livonian Crusade in the territories comprising present day Estonia and Latvia. It was established on 2 February 1207, as a principality of the Holy Roman Empire but lost this status in 1215 when proclaimed by Pope Innocent III as directly subject to the Holy See.

Terra Mariana was divided into feudal principalities by Papal Legate William of Modena:

After the 1236 Battle of Saule the surviving members of the Brothers merged in 1237 with the Teutonic Order of Prussia and became known as the Livonian Order. In 1346 the Order bought Danish Estonia. Throughout the existence of medieval Livonia there was a constant struggle over supremacy, between the lands ruled by the Church, the Order, the secular German nobility and the citizens of the Hanseatic towns of Riga and Reval. Following its defeat in the Battle of Grunwald in 1410 the Teutonic Order and the Ordenstaat fell into decline but the Livonian Order managed to maintain its independent existence. In 1561, during the Livonian war, Terra Mariana ceased to exist. Its northern parts were ceded to Sweden and formed into the Duchy of Estonia, its southern territories became part of the Grand Duchy of Lithuania — and thus eventually of the Polish–Lithuanian Commonwealth — as the Duchy of Livonia and the Duchy of Courland and Semigallia. The island of Saaremaa became part of Denmark.