What did the presence of multi-story stone houses made of coral in Swahili cities signify?

A lack of local timber and building resources

A nomadic lifestyle requiring temporary structures

The wealth, permanence, and stability of the society

A cultural preference for living in fortified compounds

The Swahili city-states were politically organized as a...

single, unified empire under one emperor.

series of independent and competing port cities.

collection of vassal states loyal to a Persian king.

group of nomadic tribes with no central authority.