The original Castle was built of timber and was fortified with a soil rampart. The castle grounds were as large then as�they are�today and consisted of many small timber houses. This was found quite by accident, Third Square, the oldest part of the castle was being rebuilt in 1920, when the walls of older buildings were uncovered. Archaeological excavation uncovered many important finds concerning Prague Castles' history. This area originally was kept partially open to the public, but today the excavation area has been walled, and it is probably the most extensive researched archaeological site in central Europe.

The first stone buildings were built much later. The oldest church, the Basilica of St. George, is one of the few Roman churches that still has remains of the previous�stone building inside. The church has contained the relics
of the Premyslid Princes and family members, along with relics of St. Ludmilla, the first saint and national patron, since it was built.