Master Conrad von Thierberg used the fortress as a base for further campaigns along the Neman River and against Samogitia. Memel was unsuccessfully besieged by Sambians in 1255, and the scattered Sambians submitted by 1259. Memel was colonized by settlers from Holstein, Lübeck and Dortmund, hence Memel also being known at the time as "Neu-Dortmund", or "New Dortmund". 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. According to different sources, Memel received Lübeck city rights in 1254 or 1258.