His reign is remarkable for the degree to which Egypt exploited its resources. Mining camps in the Sinai, which had previously been used only by intermittent expeditions, were operated on a semi-permanent basis, as evidenced by the construction of houses, walls, and even local cemeteries.[45] There are 25 separate references to mining expeditions in the Sinai, and four to expeditions in Wadi Hammamat, one of which had over two thousand workers.[46] Amenemhet reinforced his father's defenses in Nubia[47] and continued the Faiyum land reclamation project.[48] After a reign of 45 years, Amenemhet III was succeeded by Amenemhet IV,[45] whose nine-year reign is poorly attested.[49] Clearly by this time, dynastic power had begun to weaken, for which several explanations have been proposed. Contemporary records of the Nile flood levels indicate that the end of the reign of Amenemhet III was dry, and crop failures may have helped to destabilize the dynasty.[48] Further, Amenemhet III had an inordinately long reign, which tends to create succession problems.[50] The latter argument perhaps explains why Amenemhet IV was succeeded by Sobekneferu, the first historically attested female king of Egypt.[50] Sobekneferu ruled no more than four years,[51] and as she apparently had no heirs, when she died the Twelfth Dynasty came to a sudden end as did the Golden Age of the Middle Kingdom.