The Orkhon is the longest river in which of the following countries?

Many people picture Mongolia as little more than an expansive desert or sprawling plains edged by rugged mountains. However, several key rivers feed the plains, creating fertile grazing lands, which are inhabited by the nation's nomadic peoples.

The longest of these rivers is the Orkhon, or Orhon. The river’s name comes from the Old Turkic prefix "or" meaning "middle", and "khan" or king. Contained entirely within Mongolia, the river rises in the Khangai Mountains to the south, then winds its way in a northeasterly direction for nearly 700 miles (1,124 km), before flowing into the Selenge River near the Russian border. The Selenge then flows further north into Russia and Lake Baikal.

Fish found in the river include pike, carp, perch, taimen and catfish. The Orkhon is navigable, however, due to the region's harsh climate, only shallow-bottom vessels are able to travel it during the months of July and August.

There are two sets of ancient ruins along the river valley: Khar Balgas, the ancient capital of the Uyghur Kingdom, and Karakorum, the ancient capital of the Mongol Empire. Several imperial tombs in the river valley area were excavated in the 1920s by Pyotr Kozlov, a Russian/Soviet explorer.

Today, UNESCO lists the Orkhon Valley as a World Heritage Site. The acronym stands for United Nations Education, Scientific and Cultural Organization. The organization’s stated purpose is to help identify and protect important cultural and natural places all over the world.