The Tigris-Euphrates Valley was the site of the world's first civilization. The valley follows the Tigris and Euphrates rivers north and west from the Persian Gulf, in what is now Iraq. The people of the civilization are known as Sumerians. The Sumerians built cities and invented a method of writing called <I>cuneiform.</I> They used their writing to inscribe clay tablets. The Sumerians traded widely with other peoples, including the Egyptians. They also developed a complicated system of laws governing weights, measures, and trading.<NP> For more information, see the section <I>The Tigris-Euphrates Valley</I> in WORLD, HISTORY OF THE.
