Städtebund

A league of towns (in German: Städtebund) is an alliance of two or more, usually geographically close, towns and/or cities for the protection of their political and/or economic interests.

The term predominantly refers to medieval leagues of towns (since the 13th century), which usually became important economic, political and even religious factors in their respective countries, but it is also used for the ancient world and for modern town alliances.

Examples: Rheinischer Städtebund

...
Wikipedia