On the basis of archeological research and the oldest written sources it is thought that Prague Castle was founded around the year 880 by Prince Borivoj of the house of Premyslides. The early medieval castle site was fortified with a moat and a rampart of clay and stones. The first walled building was the church of Our Lady. Other churches, dedicated to St. George and St. Vitus, were founded in the first half of the 10th century. From the 10th century Prague Castle was not only the seat of the head of state, the princes and later kings, but also of the highest representative of church, the Prague bishop. The first convent in Bohemia was also founded in the grounds of Prague Castle, a convent next to the church of St. George for the order of Benedictine nuns. The basilica of St. Vitus, built on the site of the original rotunda, was the main castle church since the 11th century, where the relics of the patron saints of the land were kept: SS. Vitus, Wenceslas and Adalbert. And from the 10th century the convent of the Prague church was an important educational and cultural institution.