The Jacobi Expedition was an exploration into the Duat led by Jacobi Henry, it began in A.Y. 279. Ostensibly, the expedition was in search of gold, but Jacobi's true motive was to map at least a large portion of the Duat and to potentially establish underground colonies. Land on the surface was at something of a premium, but space underground, it seemed, was plentiful.
Jacobi's party consisted of a thousand man, fifteen hundred horses, seven hundred specially-designed wagons, and a huge backing from various organizations on the surface. The group carried enough food for an entire year, with the plan being to thoroughly map everywhere they went and establish supply-lines. Eventually, Jacobi planned to construct a mining colony of three thousand when they made a suitable strike.
The expedition began at a Duat entrance located on the eastern edge of the Agras Plains. The exact location of Jacobi's entrance has since been lost, and was a well-kept secret even in its time.
Accounts from the journey indicate it was very difficult. The original descent took months; getting the horses and wagons and all of the supplies down through a series of deep crevices was not at all an easy matter. Forward progress was equally challenging; every time the party had to cross a gorge or ford an underground river, it was a massive undertaking. Still, Jacobi's journals report they never lost a single man to an accident.