Karlštejn Castle was founded in 1348 by the Charles IV, King of Bohemia and Holy Roman Emperor as his private residence and a place of safekeeping royal treasures, especially his collections of holy relics and the Imperial Crown Jewels. In 1355 Charles IV stayed here for the first time, overseeing the construction and decoration work, especially in chapels. The construction was completed in 1365 when the Chapel of the Holy Cross in the Great Tower was consecrated. The Chapel of the Holy Cross was the place of safekeeping the imperial crown jewels until 1420 when the Hussite wars (religious civil war) began, and they had not ever returned to Karlštejn Castle. After the wars in 1436, the Bohemian crown jewels were taken to the Chapel of the Holy Cross where they remained till 1619.
The castle was a representative residence of Charles IV and his son Wenceslas IV only, i.e. till 1419. As a fortress, Karlštejn Castle protected the crown jewels, holy relics, and royal archives till the 17th century.
Over the centuries the castle has always been in hands of the king or a state institution, never in private hands. Nowadays it is owned by the state.