A circular fortress located in the province of Timimoun, near the ksar of Drâa in the Algerian desert, has intrigued researchers for centuries. The structure, which stands about nine meters high and has walls over 1.80 meters thick, features a single door with no inscriptions that reveal who built it. Estimated to be at least 700 years old, the fortress does not match any known Berber ksar model in the region. The term "ksar" usually describes a fortified village common among Berber communities, often found in mountainous areas and made up of a cluster of connected houses. However, this ksar is different, as it is circular in shape and located in the open desert, away from the usual mountainous terrain. No inscriptions, hieroglyphs, or other direct clues about the builders or the original use of the site have been discovered. Several theories attempt to explain the fortress’s function. One theory suggests it was a natural prison, with the surrounding dunes and single door making escape extremely difficult. Another theory proposes it was a fortified village built to protect its inhabitants from the harsh desert conditions. A third theory, backed by National Geographic, suggests it may have been a caravanserai—a type of roadside inn—used by trans-Saharan travelers. This idea is supported by the structure's architectural features, which resemble those of traditional caravanserais, including strong walls, a single entrance, and possible storage areas and stables. Despite these theories, no definitive evidence has been found to confirm the fortress’s original purpose. The interior of the ksar could have contained homes, a mosque, communal kitchens, or even a school, but these ideas remain unconfirmed due to the lack of sufficient material evidence. The site is considered one of Algeria’s most valuable archaeological treasures, and the debate over its purpose continues to this day.