Searching for Merlin's weapon that would destroy ascended beings, SG-1 visited Camelot on PX1-767. There they were told that the Sangreal, the Holy Grail that was the key to Merlin's device, was no longer there, but that King Arthur and his knights had left to quest for the Sangreal long ago. It was said that they had journeyed to three distant lands mentioned in Merlin's prophecy: Castiana, Sahal, and Vagon Brei.
Daniel turned to the library database in Atlantis to search for the locations of Castiana and Sahal, but he discovered that he was speaking not to a holographic interface but rather to Morgan Le Fay herself, who gave him the answers he sought. Although Castiana and Sahal were the names of the two planets in Old English, their Ancient names were Taoth Vaclarush and Valos Cor, and Morgan provided the two addresses: 29-3-6-9-12-16 and 29-18-19-20-21-22.
Search parties were sent to Castiana, but its atmosphere had become toxic, and no evidence of the Sangreal was found. However, Daniel noticed that the coordinates of the three planets formed an equilateral triangle, and the addition of PX1-767 as a departure point formed a tetrahedron, a perfect pyramid, a discovery that suggested more than coincidence. A computer search of permutations for planetary designations made up of symbols from all three addresses returned only one result, and SG-1 journeyed next to that world to continue their quest.
Stargate Coordinates for Castiana and Sahal: 29-3-6-9-12-16 and 29-18-19-20-21-22