In 1957, carved and painted segments of walls were discovered near the northern part of the cathedral. They turned out to be the ruins of the Chapel of Saint George. The sanctuary of the chapel, which is referred to several times in the medieval diplomas, was horseshoe shaped. The head relic of Saint George, which King Saint István (Stephen I of Hungary) received from the Byzantine emperor as a present in memory of his victory over the Bolgars in 1016-18, was kept here. It is mentioned in the Legend of Saint Imre, which was written between 1109 and 1112. During the excavation, a round church (rotunda) was found under the 13th century chapel. The red marble tombstone of Bishop Albert Vetési, the leading diplomat of King Matthias, can be seen here. In 1473, the bishop had the chapel repainted and had a red marble Gothic altar constructed in it. The chapel also served as a chapter house, and according to a diploma issued in 1417 it was also the site of elections of bishops.