The cardiovascular system 21 the heart, blood vessels, and blood. From the heart, blood travels into the arteries and their smaller branches. It continues to the capillaries. Then, it moves to the branches of the vein 22 to the heart. The heart serves as a pump. Arteries transport blood from the heart to body organs and tissues. Veins transport blood back to the heart.

   Mesopotamia, meaning “land between the rivers,＂ is widely considered to be the cradle of civilization. It was here, in 5000 B.C., that people settled into an agricultural lifestyle by the mighty Tigris and Euphrates rivers. Because there was little rain, the people depended on these rivers for their survival. The Mesopotamians created channels to distribute the flood waters that flowed for a short duration each year to their crops. The efficiency of their irrigation systems allowed their society to flourish, enabling them to create the world＇s first towns and cities. At the center of each town stood a temple complex with food stores, a treasury, and living spaces, all of which were incorporated into the overall design. Over time, these towns evolved into city-states, eventually becoming an empire.

   Soon there arose a need to keep reliable records of commodities traded, and out of this need, writing was born. The first format that writing took was a code of symbols which corresponded to various items and numbers. These were carved into soft clay and were known as cuneiform. This system proved to be very versatile and quickly spread to other uses. The Sumerian scribes used it to record daily life and to write the first major literary work known to Western civilization. Perhaps the best known of Mesopotamia＇s civilizations was Babylon. During the second millennium B.C., it rose from a regional capital to become the center of a kingdom that stretched across southern Iraq and beyond. Its king, Hammurabi, left his mark with a remarkable collection of laws. Hammurabi＇s code defined the constraints of private property, as well as legal decisions for crimes, and family disputes.

   Although it was eventually lost to the sands of time, Mesopotamia left a legacy of law, literature, and engineering for modern civilizations to build on. In fact, much of what we know of that chapter in the region＇s history has come from excavations of ruined cities, supplemented by translations of ancient clay tablets.