The Eye of Ra is one of six jeweled artifacts of enormous power. According to legend, there were six Eyes, including those held by Ra, Apophis, Osiris, and Tiamat. Each is powerful on its own, but used in combination, the power is increased tenfold. The Eye of Ra had been hidden away in the catacombs of Ra's pyramid on Abydos. When Anubis managed to acquire five of the six Eyes, he came to Abydos in search of the Eye of Ra. SG-1 was able to find the Eye first, within a secret chamber with the inscription, "Rays of the sun reveal all." Surrounded by Anubis's forces, Daniel made a deal with Anubis, to trade the Eye of Ra for the safety of Abydos and SG-1. However, once in possession of the sixth Eye, Anubis used its power to create a superweapon with which he destroyed Abydos and the collective forces of the System Lords.
Cross Reference: Abydonians, Abydos, Anubis, Anubis's Superweapon, Eye of Tiamat, Ra
Episode Reference: Full Circle