Year 1520 (MDXX) was a leap year starting on Sunday (link will display the full calendar) of the Julian calendar. Events January–June January 19 – King Christian II of Denmark and Norway defeats the Swedes, at Lake Åsunden in Sweden. The Swedish regent Sten Sture the Younger is mortally wounded in the battle. He is rushed towards Stockholm, in order to lead the fight against the Danes from there, but dies from his wounds on February 3. April 16 – Revolt of the Comuneros: Citizens of Toledo, Castile opposed to the rule of the Flemish-born Charles V, Holy Roman Emperor, rise up when the royal government attempts to unseat radical city councilors. June – Moctezuma II, Aztec ruler of Tenochtitlan, is declared deposed due to his captivity by conquistador Hernán Cortés. His brother Cuitláhuac rises to the throne. June 7 – King Henry VIII of England and King Francis I of France meet at the famous Field of the Cloth of Gold. June 10 – Revolt of the Comuneros: Segovia is blockaded. June 15 – Pope Leo X issues the bull Exsurge Domine (Arise O Lord), threatening Martin Luther with excommunication, if he does not recant his position on indulgences and other Catholic doctrines. July–December July 1 – La Noche Triste (Night of Sorrow): The forces of Cuitláhuac, Aztec ruler of Tenochtitlan, gain a major victory against the forces of conquistador Hernán Cortés. This results in the death of about 400 conquistadors, and some 2,000 of their Native American allies. However, Cortés and the most skilled of his men manage to escape and later regroup. July 7 – Otumba near Lake Texcaco: The Spaniards defeat the Aztecs. August – Martin Luther writes To the Christian Nobility of the German Nation. September 7 – Christian II makes his triumphant entry into Stockholm, which had surrendered to him a few days earlier. Sten Sture's widow Christina Gyllenstierna, who has led the fight after Sten's death, and all other persons in the resistance against the Danes, are granted amnesty and are pardoned for their involvement in the resistance. September 22 – Suleiman I succeeds his father Selim I as Sultan of the Ottoman Empire. October – Cuitláhuac, Aztec ruler of Tenochtitlan, dies from smallpox. He is succeeded by his nephew Cuauhtémoc. October 21 (Feast of St. Ursula) – The islands of Saint Pierre and Miquelon are discovered by Portuguese explorer João Álvares Fagundes,