- The Tyrrhenian Sea (/tɪˈriːniən, -ˈreɪ-/, tih-REE-nee-ən ,-RAY-; Italian: Mar Tirreno [mar tirˈrɛːno] or [-ˈreː-]) is part of the Mediterranean Sea off the western coast of Italy. Its namesake is from the Tyrrhenian people, identified with the Etruscans of Italy.