Careful observations of the heavens appear to have been important for nomadic pastoralists who moved across the Western Sahara Desert during the Late Neolithic. Evidence for their interest in astronomy is found in the ceremonial complex they built on the western shores of Nabta Playa some 2000 years before construction of similar megalithic structures at Stonehenge and elsewhere in northern Europe. These nomads moved across trackless oceans of sand, and they must have found the stars to be as useful for navigation as did those who attempted to find their ways across the Pacific and Atlantic oceans. Ultimately they were drawn to Nabta playa because of the promise of water, which began to accumulate in Nabta Playa around the time of summer solstice. It should come as no surprise that in the astronomy displayed by the ancient stones of Nabta are contained the two most powerful celestial phenomena in the lives of these people: the rising of the sun at summer solstice, associated with the onset of summer rains, and the organization of the stars at night into patterns that could guide them across the desert.
Located 100 km west of Abu Simbel in southern Egypt, Nabta Playa is a large internally drained basin, which during the period 11,000 to 5000 years before the present was an important ceremonial center for prehistoric people (Malville et al1998; Wendorf et al 1992-3). During the season when it was filled by summer monsoon rains the western shore of the lake was visited by nomadic pastoralists who came to water and feed their animals as well as record astronomical events, erect lines of megaliths in the sediments of the lake, and construct impressive stone structures.
From about 65,000 years ago until about 12,000 years ago the Western Desert was hyper-arid, at least as dry as today and perhaps even drier. Changes began when the summer rains of tropical Africa began to move northward, bringing sufficient moisture for variety of sahelian grasses, tress, and bushes to grow and for a few small animals to exit, mostly hares and small gazelle, but also small carnivores. Even with the summer rains, it was still very dry with an annual rainfall no more than 10-15 cm. There were times of serious droughts, some of which resulted in the abandonment of the desert for extended periods.
The earliest (11,000-9300) settlements composed of seasonal camps of cattle-herding and ceramic-using people. These cattle must have been domestic, as they could not have existed in the arid landscape without human assistance. In a manner similar to that of central Africa today, cattle may have functioned as walking larders, which provided milk and blood. Meat may have been reserved for ceremonial occasions. Cattle also provided prestige and may have been major agents in the stratification of nomad society, as they are today in Central Africa. These early people probably came into the desert after the summer rains from farther south or from the Nile Valley in search of pasture; in the fall when the surface water in the playa dried up they had to return to the Nile or to better watered area in the south.
Part of the record they left in the sand are countless stones scattered across the dunes at the western edge of the lake; these stones are fire reddened due to oxidization of iron and were initially carried into the area to line fire pits and hearths. As the winds pulled sand away from the pits, the stones became scattered across the dunes, some of which have been stabilized by their "skin" of old hearths.
By 9000 years ago, the settlements around Nabta were larger and some of the inhabitants were able to live in the desert year around by digging walk-in wells, providing water for them and their domesticated animals. Around 7500 years ago a major change occurred in the character of the Neolithic society at Nabta. In their periodic movement, synchronized with the summer rains, they established a pattern of movement across the landscape that paralleled the heavenly cycle of the sun in the sky, and these nomads may have become some of the worlds first pilgrims. Their repetitive movement over the millennia into Nabta may have eventually acquired a deeper meaning and significance than simply a search for food and water.
The groups who returned to the desert at summer solstice had a complex social structure associated with a degree of organization and control not previously seen in Egypt. These people sacrificed young cows and buried them in clay-lined and roofed chambers. They placed lines of large (2x2x4 meters) roughly shaped sandstone slabs in the sediments of the lake.
One of the megalithic alignments is parallel to the rising point of Sirius, the brightest star in the night sky. For people standing on the shore of the lake in the early morning hours around summer solstice, the brilliant and flickering Sirius rising along the megalithic alignments, its light reflected in the surface of the lake, must have been a stunning sight. In the calendar circle, they built Egypts earliest astronomical measuring device, which marks the rising position of the sun at summer solstice. Also at the western edge of the playa, they constructed some 30 megalithic structures, consisting of both surface and subterranean megalithic structures, consisting of both surface and subterranean features. A shaped stone, which bears some resemblance to a cow, was unearthed from one of these megalithic structures, and it may be the oldest known sculpture in Egypt.
We understand a regional ceremonial center to be a place where related but widely separated groups gather periodically to conduct ritual and to reaffirm their social and political cohesion. Today in Africa ceremonial centers foster social integration though their religious, political, and social activities. The presence of ceremonial structures at Nabta may indicate that the desert people were more highly organized and more astronomically knowledgeable than their contemporaries in the Nile Valley.
The possibility of connections between the cattle pastoralists in the Sahara and the Neolithic groups in the Nile Valley raises the intriguing, though highly speculative, possibility that social and symbolic complexity of the Saharan pastoralist societies may have contributed to the development of high culture along the Nile.
The roles of cattle in these two cultures may offer a clue. Among the ancient Egyptians cattle were deified and regarded as earthly representative of the gods. The cow goddess, Hathor, was the mother of the sun as well as the mother of Horus, of whom pharaohs were understood to be the embodiment. In spite of this symbolic significance of cattle in the Old Kingdom, they did not play a significant role in the economy. Cattle worship may have been part of the heritage passed on by Saharan pastoralists to the great kingdoms of the Nile Valley.
There are six megalithic alignments extending across the sediments of the Playa, containing a total of 24 megaliths or megalithic scatters. Like the spokes on a wheel each alignment radiates outward from the complex structure A (Figure 1). According to our analysis, these lines coincide with the rising positions of three prominent stars during the period 4800-3700 B. C.: Sirius (the brightest star of the night sky), Dubhe, (the brightest star in Ursa Major), and stars in the belt of Orion.
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