Carved into the stone bas-reliefs of the Portal of Judgment — the great central western portal — are circular medallions that Fulcanelli read as the alchemical Great Work (Magnum Opus):
The Alchemist holding the Athenor. On the central pillar sits a carved figure of an alchemist holding an Athenor furnace in one hand and the Hermetic flask (Vas Hermetis) in the other, gazing upward at the rose window geometry.
The Serpent of Caduceus & Dragon. Medallions showing the dual energetic serpents (Fixed and Volatile) wrapped around a central staff.
Each carries its full hermetic decipherment and an observational protocol — where to stand, when, and what to watch for — in the Paris field codex.
Or read the complete Florence codex free first.