Which river is known as the eastern river defining ancient Mesopotamia?

The Tigris River is recognized as the eastern river that helped define ancient Mesopotamia, an area that is often referred to as the "Cradle of Civilization." This river, along with the Euphrates, is crucial in the region's geography and history. Together, these rivers provided fertile land and water resources that supported agriculture and the emergence of some of the world's earliest urban centers, such as Uruk and Babylon.

The Tigris flows through modern-day Iraq and is essential for irrigation, which allowed for the sustenance of large populations in ancient times. The dual-river system of the Tigris and Euphrates contributed to the development of complex societies in Mesopotamia, setting the stage for advancements in writing, trade, and governance.

The Euphrates River also played a significant role in Mesopotamian history, but the Tigris is specifically noted as the eastern boundary. The Indus River is located in the Indian subcontinent and is unrelated to Mesopotamian civilization, while the Jordan River is situated in the Levant, further to the west. Understanding the geographical relevance of the Tigris helps clarify its importance in the context of ancient Mesopotamia.