Terra Mariana was the formal name for Medieval Livonia or Old Livonia. It was formed in the aftermath of the Livonian Crusade, and its territories were composed of present-day Estonia and Latvia. It was established on 2 February 1207, as a principality of the Holy Roman Empire, and lost this status in 1215 when Pope Innocent III proclaimed it as directly subject to the Holy See.

The Livonian crusade consists of the various military Christianisation campaigns in medieval Livonia – modern Latvia and Estonia – during the Papal-sanctioned Northern Crusades in the 12–13th century. The Livonian crusade was conducted mostly by the Holy Roman Empire and the Kingdom of Denmark. It ended with the creation of Terra Mariana and the Danish duchy of Estonia. The lands on the eastern shores of the Baltic Sea were one of the last parts of Europe to be Christianised. The available information is largely based on Livonian Chronicle of Henry.