The House of Czartoryski (feminine form: Czartoryska, plural: Czartoryscy; ) is a Polish princely family of Lithuanian-Ruthenian origin, also known as the Familia. The family, which derived their kin from the Gediminids dynasty, by the mid-17th century had split into two branches, based in the Klevan Castle and the Korets Castle, respectively. They used the Czartoryski coat of arms and were a noble family of the Polish–Lithuanian Commonwealth in the 18th century. The Czartoryski and the Potocki were the two most influential aristocratic families of the last decades of the Polish–Lithuanian Commonwealth (1569–1795). History The Czartoryski family is of Lithuanian descent from Ruthenia. Their ancestor, a grandson of Gediminas, the Grand Duke of Lithuania, became known with his baptismal name Constantine ( 1330−1390) - he became a Prince of Chortoryisk in Volhynia. One of his sons, Vasyli Chortoryiski (Ukrainian: Чарторийський; 1375–1416), was granted an estate in Volhynia in 1393, and his three sons John, Alexander and Michael (c. 1400–1489) are considered the progenitors of the family. The founding members were culturally Ruthenian and Eastern Orthodox; they converted to Roman Catholicism and were Polonized during the 16th century. Michael's descendant Prince Kazimierz Czartoryski (1674–1741), Duke of Klewan and Zukow (Klevan and Zhukiv), Castellan of Vilnius, reawakened Czartoryski royal ambitions at the end of the 17th century. He married Isabella Morsztyn, daughter of the Grand Treasurer of Poland, and built "The Familia" with their four children, Michał, August, Teodor and Konstancja. The family became known and powerful under the lead of brothers Michał Fryderyk Czartoryski and August Aleksander Czartoryski in the late Polish–Lithuanian Commonwealth of the 18th century, during the reigns Augustus II the Strong (King of Poland, 1697-1706 and 1709-1733) and Stanisław I Leszczyński (King of Poland 1704-1709 and 1733-1736). The Czartoryski had risen to power under August Aleksander Czartoryski (1697–1782) of the Klewa line, who married Zofia Denhoffowa, the only heir to the Sieniawski family. The family attained the height of its influence from the mid-18th century in the court of King Augustus III (. The Czartoryski brothers gained a very powerful ally in their brother-in-law, Stanisław Poniatowski, whose son became the last king of the independent Polish-Lithuanian Commonwealth, Stanisław August Poniatowski (). The Czartoryski's Familia saw the decline of the Commonwealth and the rise of anarchy and joined the camp which was determined to press ahead with reforms; thus they sought the enactment of such constitutional reforms as the