Pustý hrad is a castle whose ruins are located on a forested hill near Zvolen in central Slovakia. With an area of 76,000 m² it is arguably one of the largest medieval castles in Europe. The original name was Zvolen Castle or Old Zvolen; Pustý hrad (meaning "deserted castle") is a much later name used to distinguish the ruin from the present-day Zvolen Castle.
The site upon the river Hron attracted settlers as early as during the Bronze Age and the Iron Age, when the first fortifications in the area were built. The ongoing excavations have unearthed many precious artifacts from those periods, including several big bronze treasures of the Lusatian culture and pottery imported from the Roman Empire. The subsequent Slavic medieval castle was founded in the 9th century.
As a regional center, it was incorporated into the Kingdom of Hungary and it became a seat of a county. The oldest stone buildings (for example the keep) are attributed to King Bela III. In the 12th century, an exceptionally large area of the present castle was fully fortified in order to protect eventual refugees from Zvolen in case of a Mongol invasion. In addition to an older keep (50 metres tall), another one was built. Subsequent development was connected with Magister Knight Donč, a noble warrior and diplomat serving to Charles I of Hungary. Under the influence of his journey to France, Donč built a significant extension (a "Lower Castle") and ordered a Gothic modernization.
The castle lost its importance in the 15th century and it was ruined by fire during a siege in 1452. Since 1992 there are important archeological works on these ruins lead by Dr. Václav Hanuliak. Some parts of the castle have been therefore recently reconstructed.