Within the framework of a Franco-Lebanese mission in the area of Tyre (Lebanon), we were able to improve our knowledge of the relative sea level variations on its maritime facade. Two fish tanks were discovered near the southern and northern capes of the ancient rocky island of Tyre. Both fish tanks were cut into a Pleistocene sandstone bedrock. Small water inflow and outflow channels, also cut into the sandstone bedrock, help to better understand and constrain the variations in relative sea level during ancient times in this area. The first results show that these Roman fish tanks were affected by a relative sea-level rise of ca. 0.50 m. This 0.50 m rise is usually observed around the Circum-Mediterranean since the Roman period. In other words, no tectonic movement appears to have affected this area since Roman times.