<P> The Great Wall of China visible today largely dates from the Ming dynasty, as they rebuilt much of the wall in stone and brick, often extending its line through challenging terrain . Some sections remain in relatively good condition or have been renovated, while others have been damaged or destroyed for ideological reasons, deconstructed for their building materials, or lost due to the ravages of time . For long an object of fascination for foreigners, the wall is now a revered national symbol and a popular tourist destination . </P> <P> The conflict between the Chinese and the nomads, from which the need for the Great Wall arose, stemmed from differences in geography . The 15" isohyet marks the extent of settled agriculture, dividing the fertile fields of China to the south and the semi-arid grasslands of Inner Asia to the north . The climates and the topography of the two regions led to distinct modes of societal development . </P> <P> According to the model by sinologist Karl August Wittfogel, the loess soils of Shaanxi made it possible for the Chinese to develop irrigated agriculture early on . Although this allowed them to expand into the lower reaches of the Yellow River valley, such extensive waterworks on an ever - increasing scale required collective labour, something that could only be managed by some form of bureaucracy . Thus the scholar - bureaucrats came to the fore to keep track of the income and expenses of the granaries . Walled cities grew up around the granaries for reasons of defence along with ease of administration; they kept invaders out and ensured that citizens remained within . These cities combined to become feudal states, which eventually united to become an empire . Likewise, according to this model, walls not only enveloped cities as time went by, but also lined the borders of the feudal states and eventually the whole Chinese empire to provide protection against raids from the agrarian northern steppes . </P> <P> The steppe societies of Inner Asia, whose climate favoured a pastoral economy, stood in stark contrast to the Chinese mode of development . As animal herds are migratory by nature, communities could not afford to be stationary and therefore evolved as nomads . According to the influential Mongolist Owen Lattimore this lifestyle proved to be incompatible with the Chinese economic model . As the steppe population grew, pastoral agriculture alone could not support the population, and tribal alliances needed to be maintained by material rewards . For these needs, the nomads had to turn to the settled societies to get grains, metal tools, and luxury goods, which they could not produce by themselves . If denied trade by the settled peoples, the nomads would resort to raiding or even conquest . </P>

Why did they build the wall of china