The Tigris and Euphrates are the two great rivers of Southwest Asia that define Mesopotamia, the 'land between the rivers.' Both rivers originate in the mountains of eastern Turkey and flow through Syria and Iraq before merging to form the Shatt al-Arab, which empties into the Persian Gulf. Historically, these rivers were the foundation of the 'Fertile Crescent,' where the world's first urban civilizations, like Sumer and Babylon, emerged. The rivers are characterized by their unpredictable flooding, which necessitated the early development of complex irrigation and dam systems. Today, the rivers are at the center of regional water disputes, as dam construction in Turkey (the GAP project) has significantly reduced water flow to downstream Iraq and Syria. The marshlands of southern Iraq, located where the rivers meet, are a UNESCO World Heritage site and home to the unique Marsh Arab culture.