What does the suffix burg (‘borough’, in English) mean when added to place names?
The incidence of these words as suffixes to place names usually indicates that they were once fortified settlements.
Hamburg, Lüneburg and Duisburg are not fortified settlements anymore, but modern cities located in western and northern Germany.
Even if they have common origins, they look quite different from each other today.
Hamburg is a cosmopolitan harbour city at the Elbe estuary;
Duisburg is a workers’ city in the centre of the Rhine-Ruhr industrial area;
And Lüneburg is a small old city kept out of the air raids of the World War II.