Buhen - The most famous of a line of forts built by Pharaoh Sesostris III in southern Egypt to defend its border with Kush (that is Nubia). Originally a settlement founded during the Old Kingdom, the fort was later built around it. Situated on the West bank of the Nile, its walls were five meters thick and ten meters high. They stretched 500 meters along the length of the river and were 200 meters deep. Due to its size, it probably served as more than just a military outpost; likely protecting Egyptian trade as well. It was actually captured by the Kushites during the 13th Dynasty and held for almost two centuries before the Egyptians took it back. Today the fort lies under hundreds of feet of water as Lake Nasser was created when the Aswan Dam was built in 1964. But before it went to its watery grave, it was excavated. It's design is pretty sophisticated for such an ancient fort; protected by a moat and drawbridges, battlements, bastions, buttresses and loopholes.