Mesopotamia, known as the "Land Between the Rivers", was an early civilization located in modern day Iraq that developed between the Tigris and Euphrates Rivers. It was one of the earliest areas of human settlement and agriculture, with cities like Sumer developing complex irrigation systems and growing to populations over 100,000 people by 3000 BCE. Mesopotamian civilization made many advances, such as creating one of the earliest systems of writing called cuneiform and developing codes of law under rulers like Hammurabi of Babylon. Mesopotamian society was patriarchal and divided into social classes, but also engaged in international trade and cultural exchange with neighboring groups.