The Webway Project was the Emperor's greatest secret: a colossal undertaking beneath the Imperial Palace to breach and tame the ancient alien network of the Webway, and so grant humanity swift travel among the stars without the perils of the warp. Success would have freed mankind from reliance on treacherous empyric passage and, in time, from the very need for the Astronomican.
To achieve it the Emperor withdrew from the Great Crusade, labouring in hidden vaults while the Mechanicum toiled and a great psychic gate was raised beneath Terra. It was for this work, above all, that He left the war in Horus's hands — a decision whose consequences would prove catastrophic.
The project's ruin came when Magnus the Red, breaking the Emperor's wards to warn Him of the heresy, shattered the protective barriers guarding the human portion of the Webway. Daemons poured through the breach, and what had been humanity's brightest hope became a besieged front against hell itself. The Emperor was forced to hold the gate in person, chaining Himself to His task while the galaxy burned — a foreshadowing of the eternal vigil upon the Golden Throne that His victory over Horus would demand.