The Teutonic Knights built a castle in the *Pilsāts Land of the Curonians and named it Memelburg; later the name was shortened to Memel.
From 1252–1923 and from 1939–1945, the town and city was officially named Memel.
Master Conrad von Thierberg used the fortress as a base for further campaigns along the Neman River and against Samogitia.
The first time the city was mentioned as Caloypede in the letter of Vytautas in 1413, and for the third time in the Treaty of Melno of 1422 as Cleupeda.
According to Samogitian folk etymology, the name Klaipėda refers to the boggy terrain of the town (klaidyti=obstruct and pėda=foot).
Between 19, both names were in official use; since 1945 the Lithuanian name of Klaipėda has been used.
The names Memelburg and Memel are found in most written sources from the 13th century onwards, while Klaipėda is found in Lithuania-related sources since the 15th century.
It became the main town of the Diocese of Curonia, with a cathedral and at least two parochial churches, but the development of the castle became the dominant priority.