The Sumerian city-states were some of the earliest urban centers in human history, emerging around 4500 BCE in what is now southern Iraq. Each city-state, such as Ur, Uruk, and Lagash, operated independently, with its own government, laws, and deities. They were characterized by large temples, known as ziggurats, which served as religious and administrative centers. These city-states were often surrounded by walls for protection and relied on agriculture, trade, and craftsmanship for their economies. The Sumerians developed one of the first writing systems, called cuneiform, which facilitated record-keeping and communication, contributing to their cultural and technological advancements.