Malbork Castle was built in the 14th century AD by a German Catholic religious group of Crusaders called the Teutonic; It is considered one of the largest castles in the world in terms of area, and since 1997 it has been included in the UNESCO World Heritage Sites. This castle was named Marienburg, after the Virgin Mary; It was then sold by Bohemian mercenaries to the Fourth King of Poland and became one of Poland's royal residences. Malbork Castle is a classic example of a medieval castle, and is home to the Museum of Artifacts and the impressive amber collection.