Nubia is the vast region extending southward from Aswan. In antiquity, Nubia was considëred to be outside the official territory of Egypt, but Egyptian influence, Control and at times occupation, was exerted over the land and its inhabitants. There were, however, short periods during which Nubian tribes or occasional kingdoms in interfering seriously with Egyptian interests, threatened its southern borders and even conquered and ruled Egypt. The Nubian threat was a constant preoccupation of Egyptian kings, who built numerous forts at the Second Cataract (Wadi Halfa) in order to curb potential Nubian invasions, and many punitive and preventive military expeditions were sent here during the Middle and New Kingdoms. Nubia supplied many valuable materials which were coveted by the Egyptian court, including gold, ebony, ivory, panther skins, ostrich feathers and eggs. Particularly aggressive Nubian tribesmen were imported as mercenaries and policemen; others were taken as slaves. Contacts with Nubia go back to the predynastic period and Egyptian pottery (funerary) assemblages from this period, termed Croup A, were discovered there. As early as the 4th Dynasty, Egyptian installations were active at Buhen, possibly for smelting copper. Later in the Old Kingdom, Egyptian caravans reached the Dongola bend in quest of luxury goods, as attested to by accounts of these expeditions carved on the tombs of caravan leaders at Aswan. The intrusion of a new, aggressive culture (Group C) to the northern part of Nubia put a gradual stop to the trade caravans by the end of the Old Kingdom and an alternative caravan route was used to avoid contact with these people. The main forts of Wadi Halfa were built under powerful rulers of the 12th Dynasty, the most famous at Buhen and Mirgissa, and were manned by Egyptian garrisons. They served as trading points with the local population, as deterrents against Nubian invasion of Egypt, and protected the teams of workmen at the gold mines in the lateral wadis. During the Second Intermediate Period, a powerful Nubian kingdom based at Kerma assaulted the Egyptian forts and threatened the southern frontier of Egypt. King Ahmose of the 18th Dynasty reconquered Nubia, rebuilt some of the forts and imposed Egyptian culture on the local population. Egyptian governors, whose title was "King's son of Kush", were appointed. They ruled from Aniba and looked after Egyptian interests in Nubia. They built prestigious •Egyptian temples on Nubian territory including the rock-cut temple of Abu Simbel built under Ramesses Il. Many military forays, some of which reached the fourth cataract of the Nile, were undertaken by the Warrior kings (18th Dynasty). A bitter war was fought in Nubia against a King's Sön of Kush named Pinhassy, who revolted during the last years of the 20th Dynasty. Unable to win that war, the Egyptians gave up their claim to Nubia and lost the rich gold-mines of the region. The 25th Dynasty of Egypt consisted of Nubian kings who invaded Egypt and subdued its Libyan rulers. These kings renewed the tradition of royal burials in pyramids and built pyramid fields at el-Kurru and Nuri. In the Roman period, after the extinction of pharaonic rule in Egypt, a Nubian kingdom at Meroe remained active and prosperous. Many Egyptian PharaOnic elements lived on in the culture of Meroe side by side with central African customs.