Warsaw, like many Polish cities -- save for Krakow -- was mostly destroyed during World War II. Thus, the "old city" is a recreation of a certain style, for which Warsovians have an Italian painter named Bernardo Bellotto to thank.
Bellotto lived in Warsaw in the mid-1700s, and painted various cityscapes. Postwar Warsaw's city government availed of his collection of paintings to rebuild the erstwhile grandeur of the capital; you can see reproductions of his works at a handful of tourist attractions, to help you imagine the scene.