Antarctica is technically a desert — it receives less precipitation than the Sahara in many areas.

Greenland is the world's largest island.

Ancient civilizations often formed near rivers.

Mongolia is the world's least densely populated country, with about 5 people per square mile.

The Erie Canal connected the Great Lakes to the Atlantic Ocean.

The Atacama Desert in Chile is the driest non-polar desert on Earth — some weather stations there have never recorded rain.

The Maldives is the world's lowest-lying country, with an average ground level of just 1.5 meters above sea level.

The Colosseum in Rome could hold up to 80,000 spectators — comparable to a modern NFL stadium.

The Colosseum in Rome could hold between 50,000 and 80,000 spectators and had a retractable awning called the velarium.