The history of Turkmenistan is largely shrouded in mystery, its past since the arrival of Indo-European Iranian tribes around 2000 BC is often the starting point of the area's discernible history. Early tribes were nomadic or semi-nomadic due to the arid conditions of the region as the steppe culture in Central Asia was an extension of a larger Eurasian series of horse cultures which spanned the entire spectrum of language families including the Indo-Europeans and Turko-Mongol groups. Some of the known early Iranian tribes included the Massagatae, Scythians/Sakas, and early Soghdians (most likely precursors of the Khwarezmians). Turkmenistan was a passing point for numerous migrations and invasions by tribes which gravitated towards the settled regions of the south including ancient Mesopotamia, Elam, and the Indus Valley Civilization.