Cosmas of Prague (Czech: Kosmas Pražský; Latin: Cosmas Decanus; c. 1045 – October 21, 1125) was a priest, writer and historian born in a noble family in Bohemia. Between 1075 and 1081, he studied in Liège. After his return to Bohemia, he became a priest and married Božetěcha, with whom he probably had a son. In 1086, Cosmas was appointed prebendary (canonicus) of Prague, a prestigious position. As prebendary he also travelled through Europe on official matters.
His magnum opus, written in Latin, is called Chronica Boemorum ("Chronicle of Bohemians" or "The chronicle of the Czechs"). The Chronica is divided into three books:
- The first book, completed in 1119, starts with the creation of the world and ends in the year 1038. It describes the legendary foundation of the Bohemian state by the oldest Bohemians around the year 600 (Duke Bohemus, Duke Krok and his three daughters), Duchess Libuše and the foundation of Přemyslid dynasty by her marriage with Přemysl, old bloody wars, Duke Bořivoj and the introduction of Christianity in Bohemia, Saint Wenceslaus and his grandmother Saint Ludmila, reign of the three Boleslavs, the life of Saint Adalbert and bloody wars after year 1000.
- The second book describes Bohemian history for the years 1038–1092. The book starts with the heroic deeds of Duke Břetislav, known as the "Bohemian Achilles", for example with his victory over Poland. The Chronica also describes the long and great reign of King Vratislav, who was known as a forceful ruler but a brave and good man. There is also a reflection on his wars in Italy; this book ends with Vratislav's death.
- The third book (1092–1125) starts with a description of the time of instability and bloody civil wars after Vratislav's death between years 1092 and 1109. The Chronica ends with the reign of Vladislav between 1109 and 1125. The same year, 1125, Cosmas died.
Cosmas of Prague (2009). Wolverton, Lisa, ed. The chronicle of the Czechs. Washington, D.C.: Catholic University of America Press. ISBN 9780813215709. Archived from the original on 2013-10-14.