<p>It is common for rivers to change their courses from time to time throughout the geological and geomorphological history of any region in the world. However, knowing about these old courses and how the Tigris and Euphrates rivers changed in the Mesopotamian Valley is super important. That’s because Mesopotamia is where civilisation first started, and to really understand how it developed, we need to know exactly where the rivers used to flow and where they flow now, especially the Euphrates. This paper explains the possibility of obtaining accurate results about the Euphrates River’s courses in its various stages from the dawn of civilisation to the present day, relying on all available archaeological, historical and modern technical data and evidence, without neglecting any of them or relying on only one of them. Given the complexity of this subject and the intertwining of its evidence, which allowed us to identify an ancient phase of the Euphrates, we named it the ‘Ubaid - Eridu phase,’ which represents the first phase of the Euphrates before 5000 BC. Thus, the Euphrates has had six phaces with seven changes in its course since 7000 BC, after it was known to have had five phaces with six changes in its course, and the future may not stop there.</p>