Spread throughout a series of remote desert canyons in southern Jordan, Petra arose more than 2,000 years ago at the crossroads of key caravan trade routes between Arabia, Syria, Palestine, and Egypt. The Nabataeans carved most of the sprawling city's buildings, including temples, tombs, and theaters, directly into the region's towering red sandstone cliffs. Here, a Bedouin walks his camel past Petra's most famous building, Al Khazneh, or the Treasury.
Machu Picchu, Peru
The Inca had no system of writing and left no written records, and archaeologists have been left to piece together bits of evidence as to why Machu Picchu was built, what purpose it served, and why it was so quickly vacated.
In 1871, German adventurer Heinrich Schliemann began digging at Hisarlik, Turkey, (shown here) in search of the fabled city. His roughshod excavation wrought havoc on the site, but revealed nine ancient cities, each built on top of the next and dating back some 5,000 years. At the time, most archaeologists were skeptical that Troy was among the ruins, but evidence since the discovery suggests the Trojan capital indeed lies within the site.
Mohenjo Daro, Pakistan
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.