Everyone knows about the four main river valley civilizations: Egypt, Sumer, the Indus Valley, and the Yellow River Civilizations. What you may not know, however, is that there was a fifth river valley civilization. Situated in Central Asia, in a region known in antiquity as Bactria and Margiana, the Oxus Civilization, otherwise known as the BactriaMargiana Archaeology Complex, flourished between about 2250 and about 1700 BC. The civilization was in contact with everyone in the region, especially the IndoEuropean speakers living to the north, and appears to have played a major role in the migration of some of those Indoeuropeans into South Asia. The Oxus Civilization was quite literally lost to history, no records of it have survived, and it was only discovered in the 1970s by Soviet archaeologists.