The Sumerian civilization thrived in the region of Mesopotamia, which is located in present-day Iraq. Mesopotamia is often referred to as the "land between rivers" because it is situated between the Tigris and Euphrates rivers.

The climate of Sumeria was characterized by hot and dry summers and mild winters. The region experienced limited rainfall, so the Sumerians relied on the rivers for irrigation and water supply. The Tigris and Euphrates rivers provided fertile soil, allowing the Sumerians to cultivate crops such as barley, wheat, and dates.

The rivers were not only vital for agriculture but also served as transportation routes for trade and travel. The Sumerians constructed canals and irrigation systems to manage the water flow and control flooding during the rainy season.

As Sumerian villages grew in size, they transformed into large cities and established city-states. In a city-state, the city government ruled over both the city itself and the surrounding land. However, these city-states often engaged in conflicts and fought against each other. To safeguard their cities, the Sumerians constructed protective walls around them. 

The farmland, where agriculture took place, was located outside these walls. Nevertheless, in times of invasion, the people would seek safety by retreating within the city walls. Throughout Sumer, there were numerous city-states, including Eridu, Bad-tibura, Shuruppak, Uruk, Sippar, and Ur. Among them, Eridu is believed to be one of the earliest and most ancient cities in the world. 

Each city-state in Sumer had its own ruler who held different titles like lugal, en, or ensi. These rulers were similar to kings or governors, and they held significant authority. Interestingly, the ruler of the city often served as the high priest of the religion practiced in that city, which further enhanced their power and influence. Among the renowned rulers, Gilgamesh of Uruk is particularly famous. He is the central character in the Epic of Gilgamesh, one of the oldest surviving works of literature in the world.

In addition to the ruler, the Sumerian city-states had a well-organized government with officials who played vital roles in managing city construction projects and ensuring the smooth functioning of the city. The government also established laws that all citizens had to follow, and those who violated the laws faced consequences. The Sumerians are credited with inventing the concept of government, which laid the foundation for organized societies and civilizations.

Each city-state in Sumer had its own patron god or goddess, whom they worshiped and revered. At the heart of each city, there stood a magnificent temple called a ziggurat, dedicated to the city's specific deity. The ziggurat was an impressive architectural structure that resembled a stepped pyramid, with multiple levels gradually rising towards a flat top.

The ziggurat served as the religious focal point of the city-state. It was believed to be the dwelling place of the deity and a bridge connecting the earthly realm with the divine. The priests, who held significant religious authority, would conduct rituals and ceremonies on top of the ziggurat. These rituals included offerings, prayers, and animal sacrifices, all intended to please and communicate with the city god.

The Sumerian civilization made several important inventions and contributions that have had a lasting impact on human history. These inventions and contributions of the Sumerians laid the foundation for future civilizations and shaped the course of human development.