Nile River in Cairo (IMAGE) University of Texas at Austin Caption The Nile river, the longest river on Earth, flowing through Cairo, Egypt. Researchers at The University of Texas at Austin have discovered the source of the river's mysterious northward course deep in the Earth's mantle and at the same time uncovered the age of the river. Credit Nina R Usage Restrictions Include photo credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.