Events

January

• January 3 - Pope Leo X excommunicates Martin Luther in the papal bull Decet Romanum Pontificem.
• January 22 - Emperor Charles V opens the Diet of Worms.
• January 28 - Diet of Worms begins, lasting until May 25.

March

• March 6 - Ferdinand Magellan discovers Guam.
• March 16 - Ferdinand Magellan reaches the Philippines.

April

• April 7 - Ferdinand Magellan arrives at Cebu.
• April 16 - 18 - Martin Luther is examined before Emperor Charles V and the German Diet of Worms.
• April 26 - Martin Luther leaves Worms and disappears for a year - he is rumored to be murdered but really is in hiding.
• April 27 - Magellan killed in the Philippines.

May

• May - Outbreak of war between Emperor Charles and the King of France.
• May 17 - Edward Stafford, 3rd Duke of Buckingham, is executed for treason.
• May 20 - Battle of Pampeluna.
• May 25 - The Diet of Worms ends when Charles V, Holy Roman Emperor issues the Edict of Worms, declaring Martin Luther an outlaw.

June

• June 29 or June 30 - the first document fully written in Romanian: the letter of a Neacşu, a trader from Câmpulung, to Johannes Benkner, the mayor of Braşov, warning that the Ottoman Empire was preparing its troops to cross into Wallachia and Transylvania; the script used was Romanian Cyrillic.
• June 30 - Battle of Esquiroz: French forces under Henri d'Albret, exiled King of Navarre, are defeated by the Spanish and forced to abandon their attempt to recover Henri's kingdom.

August

• August 8 - Hernán Cortés and allied local Indians defeat Aztec forces of Cuautemoc, the last Aztec Emperor, in the Battle of Tenochtitlan.
• August 13 - Emperor Cuauhtémoc surrenders to Hernán Cortés.
• August 29 - Capture of Belgrade by the Ottoman army of Suleiman I after a brave resistance.

November

• November 23 - Spanish-German-Papal forces under Prosper Colonna force French Marshal Odet de Lautrec to abandon Milan.

Unknown dates

• Berengairo da Garbi notices the appendix.
• Neacsu's Letter, the oldest surviving Romanian document, was written.

Births

• March 21 - Maurice, Elector of Saxony (d. 1553)
• May 8 - Petrus Canisius, Dutch Jesuit (d. 1597)
• August 4 - Pope Urban VII (d. 1590)
• December 1 - Takeda Shingen, Japanese warlord (d. 1573)
• December 13 - Pope Sixtus V (d. 1590)
• Anne Askew, English protestant martyr (d. 1546)
• John Aylmer, English divine (d. 1594)
• Thomas Chaloner, English statesman and poet (d. 1565)
• Ottavio Farnese, Duke of Parma (d. 1586)
• Philippe de Monte, Flemish composer (d. 1603)
• Thomas Wyatt the younger, English rebel (d. 1554)

Deaths

• April 20 - Zhengde Emperor of China (b. 1491)
• April 27 - Ferdinand Magellan, Portuguese explorer
• May 10 - Sebastian Brant, German humanist and satirist (b. 1457)
• May 17 - Edward Stafford, 3rd Duke of Buckingham (executed)
• June 15 - Tamás Bakócz, Hungarian Catholic cardinal and statesman (b. 1442)
• August 27 - Josquin Des Prez, Flemish composer
• December 1 - Pope Leo X (born 1475)
• December 13 - King Manuel I of Portugal (b. 1469)
• Piero di Cosimo, Italian artist (b. 1462)
• Leonardo Loredano, Doge of Venice (b. 1436)
• Edward Poyning, Lord Deputy to King Henry VII of England (b. 1459)
• Juan Ponce de León, Spanish conquistador (b. 1460)
• Stephen Hawes, English poet (b. 1502)

1521

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