Fort Sphinxmoth (or Sphinxmoth Legion Fort) is a fortress in the Reaper's March region, in Anequina, Elsweyr. It is located north of the city of Dune, close to the border with Valenwood and Cyrodiil.
The fort was built by the Second Empire to safeguard the Elsweyr-Valenwood border from raiders, as the area was constantly plagued by warring Bosmer and Khajiit tribes. It was built into the side of a mountain to be nigh impregnable, and the halls were filled with all manner of traps. After the fall of the Second Empire, Sphinxmoth was abandoned by the legionnaires and ironically fell into the hands of the border raiders. It was traded back and forth for a generation between Bosmer and Khajiit tribes, suffering additional damage every time it changed hands, until a landslide destroyed much of the upper works and forced the ruins to be abandoned. Nothing worth looting was left in Fort Sphinxmoth, and it soon faded into obscurity as an overgrown series of tunnels.
The crocodile-infested ruins were eventually reoccupied by the Muckwater Bandits, a large bandit gang that operated out of the Muckwater and was led by an Imperial named Captain Accalia. Rebranding themselves the Sphinxmoth Bandits, the brigands repaired many of the fort's traps. During the Alliance War of 2E 582, the bandits attacked the temple of Mara in Bravil after receiving a contract from the Stonefire Cult to steal the Chalice of Mara. The priests followed the bandits back to Fort Sphinxmoth with a large contingent of temple guards, crossing into Aldmeri Dominion territory. Several guards entered the ruins in an attempt to retrieve the Chalice, along with several other holy relics, but they were all killed or captured. However, the Soulless One then entered the ruins in search of the relics and the missing guards, killing Accalia and his subordinates in the process.
Fort Sphinxmoth was later reestablished by the Imperial Legion under the Third Empire. During the Five Year War in 3E 396, a major battle took place outside the fort between the Bosmer of Valenwood and the Khajiit of Elsweyr. A soldier named Codus Callonus was stationed at the fort and was so impressed by the Khajiiti tactics during the battle that he recorded his impressions in a series of books. Unfortunately, only the first volume of Mixed Unit Tactics remains.