An Ancient tablet written by Myrddin described a hidden treasure and suggested that Myrddin was in fact Merlin, one of the Ancients who had left Atlantis and returned to Earth during the siege of the Wraith. Merlin is closely associated with King Arthur and Avalon, known today as Glastonbury.
Scholars have speculated that Arthur and Ambrosius Aurelianus may have been one and the same, although Ambrosius, the son of the Emperor Constantine, would have been 74 years old at the Battle of Mount Badon. Arthur was revered as a great warrior who once pulled a sword from a stone as proof of his righteousness and royalty, and the ritual of a sword drawn from a stone was encountered by SG-1 both in Glastonbury and in Camelot. Although it is a common misconception that the sword pulled from the stone was Excalibur, it was only after the sword from the stone broke in battle that King Arthur was given Excalibur, a sword forged by the Lady of the Lake.
According to legend, Arthur was mortally wounded in his final battle and was carried off in a barge by Merlin to the Vale of Avalon, a magical place where the dead would meet. At the time some said that Arthur never actually died but that he would in fact one day return, and Daniel speculated that Avalon could have been a place where Merlin helped Arthur, a mortal, ascend.
In 1191 the monks at Glastonbury Abbey claimed to have found the grave of King Arthur, and on the stone burial was an inlaid lead cross with the inscription, "Hic iacet sepultus inclitus Rex Artuius in insula Avallonis," ("Here lies the famous King Arthur, buried on the Isle of Avalon.") The claim was not taken seriously until 1278 when Henry II ordered the grave to be exhumed.
Conflicting interpretations of Arthur and his court suggest that the Knights of the Round Table gathered great treasures from the far corners of Arthur's domain, possibly including the Holy Grail, and hid them in a magical stronghold at Avalon. Celtic legend also says that Glastonbury Tor is hollow and contains the entrance to the Underworld - Avalon. Relying on Merlin's tablet and Celtic legend, SG-1 discovered caverns beneath Glastonbury Tor which held the hidden treasure described as the "riches of Ambrosius Aurelianus."
Cross Reference: Ancients, Glastonbury, Merlin, Merlin's Tablet, Merlin's Treasure, Sword in the Stone
Episode Reference: Avalon