Once thought (erroneously) to be a city of the biblical Queen of Sheba, Great Zimbabwe stands as the most important archaeological site yet found in sub-Saharan Africa. Though historians are still seeking answers about the origin and purpose of the city, evidence suggests the Shona, ancestors of the modern Bantu, built it beginning around A.D. 1250 and that it served as a spiritual center.

There is evidence that the ancient city of Palmyra, also known as Tadmor, was in existence as far back as the 19th century B.C. Its importance grew around 300 B.C. as trading caravans began using it as a way station between Mesopotamia and Persia. Palmyra's strategic location and prosperity attracted the interest of the Romans, who took control of the city in the first century A.D.

The Indus Valley civilization was entirely unknown until 1921, when excavations in what would become Pakistan revealed the cities of Harappa and Mohenjo Daro (shown here).

This mysterious culture emerged nearly 4,500 years ago and thrived for a thousand years, profiting from the highly fertile lands of the Indus River floodplain and trade with the civilizations of nearby Mesopotamia.