Sigismund Kęstutaitis

For other nobles of the same name, please see Sigismund.

Sigismund I Kestutian (Belarusian: Жыгімонт Кейстутавіч, Lithuanian: Žygimantas I Kęstutaitis, Polish: Zygmunt Kiejstutowicz; born after 1350, murdered 20 March 1440 in Trakai Peninsula Castle) was the Grand Prince of Lithuania from 1432 to 1440. Sigismund (transcribed as Žygimantas in Lithuanian) was his baptismal name; Sigismund's pagan Lithuanian birth name is unknown.

Son of Grand Prince of the Lithuania Kęstutis and his second wife Birutė. After the death of Kęstutis, he was a prisoner of Jogaila from 1382-1384. Sigismund was Baptised Catholic in 1383. In 1384, he escaped to the Teutonic Order to join his brother Vytautas. In 1389-1398 Sigismund was a hostage of the Teutonic Order together with his family and Vytautas family once again. He became Prince of Navahradak, 1390 - 1440, and Starodub since 1406. Participated in the Battle of Vorskla and the Battle of Grunwald. After the death of Vytautas, he supported Švitrigaila in his fight against Poland, but later was convinced to participate in a conspiracy against him.

On September 1, 1432 Sigismund became Grand Duke of Lithuania and had to accept the conditions of the Polish Crown. In 1434, he issued a privilege to nobles of Eastern Orthodox faith, making their rights equal to the rights of noble Roman Catholics. He guaranteed that no noble of Grand Duchy of Lithuania can be imprisoned and punished without a court.

Sigismund's army defeated Švitrigaila in the Battle of Pabaiskas on September 1, 1435. Livonian Order, supporting Švitrigaila, suffered a major defeat. After strengthening his positions in Lithuania, he tried to loosen this ties with Poland and started negotiations 1438-1440 with Albert II, Holy Roman Emperor but was unable to finish them, since he was killed by supporters of Švitrigaila (possibly led by Alexander Czartoryski) on March 20, 1440.