Abraxas (Gk. ΑΒΡΑΞΑΣ, variant form Abrasax, ΑΒΡΑΣΑΞ) was a word of mystic meaning in the system of the Gnostic Basilides, being there applied to the "Great Archon" (Gk., megas archōn), the princeps of the 365 spheres (Gk., ouranoi). The word is found in Gnostic texts such as the Holy Book of the Great Invisible Spirit, and also appears in the Greek Magical Papyri. It was engraved on certain antique gemstones, called on that account Abraxas stones, which were used as amulets or charms. As the initial spelling on stones was 'Abrasax' (Αβρασαξ), the spelling of 'Abraxas' seen today probably originates in the confusion made between the Greek letters Sigma and Xi in the Latin transliteration.