Query: Which cities are called Stadtstaaten, other than Bremen?
Context: Since today's Germany was formed from an earlier collection of several states, it has a federal constitution, and the constituent states retain a measure of sovereignty. With an emphasis on geographical conditions, Berlin and Hamburg are frequently called Stadtstaaten (city-states), as is the Free Hanseatic City of Bremen, which in fact includes the cities of Bremen and Bremerhaven. The remaining 13 states are called Flächenländer (literally: area states).