Having eliminated the rival dynasty at Hierakonpolis, the Theban pharaoh, Montjuhotep II, installed a garrison fortress at Abu, where he could monitor desert trading routes and create a springboard to assault an increasingly disaffected Lower Nubia, successfully annexing the region around Buhen. By c. 1872 BCE, Egypt had lost control over Wawat, precipitating a brutal assault by Amenhotep I and his co-ruler Senusret I. Nubian independence was extinguished and many conscripted into slavery. Having annexed Nubia beyond the second cataract, Senusret I embarked on a prolific fort-building programme, concentrated around Buhen and Kor. Senusret III, worried about the rebellious Kush region, established more forts and a new border between Mirgissa and Semna. Trading centres were also established along the Nile, with massive forts not only providing a display of military strength and defensive capability, but also protecting the Nile trade in gold, copper and precious metals extracted from the Nubian mines.