Klaipeda is a city in Lithuania on the Baltic Sea coast. It is the third largest city in Lithuania and the capital of Klaipeda County. The city has a complex recorded history, partially due to the combined regional importance of the usually ice-free Port of Klaipeda at the mouth of the Akmena-Dane River. It was controlled by successive German states until the 1919 Treaty of Versailles. As a result of the 1923 Klaipeda Revolt it was added to Lithuania and has remained with Lithuania to this day, except for the period between 1939 and 1945 when it returned to the Third Reich following the 1939 German ultimatum to Lithuania.