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| | 4th millennium BC - Encyclopedia, History, Geography and Biography |
 | | mb =5th millennium BC m =4th millennium BC ma =3rd millennium BC Table of Contents |
 | | Sumerian city of Ur in Mesopotamia (40th century BC); Sumerian hegemony in Mesopotamia, with the development of writing around the same time as the Indus Valley Civilization, base-60 mathematics, astronomy and astrology, civil law, complex hydrology, the sailboat, the wheel, and the potter's wheel, 4000–2000 BC. |
 | | 4th millennium BC, Events, Cultures, Environmental changes, Significant persons, Inventions, discoveries, introductions, Centuries, External references, Millennia and 4th millennium BC. |
| www.arikah.com /encyclopedia/4th_millennium_BC (601 words) |
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