Check out this 1887 map of a much smaller Rockville. This was way back when Grover Cleveland was the U.S. President, and just about two decades since the Civil War.
Source: Library of Congress
This is what the same area looks like today on Google Maps.[googlemaps https://www.google.com/maps/embed?pb=!1m14!1m12!1m3!1d6194.013237562684!2d-77.15259325211487!3d39.083546975978685!2m3!1f0!2f0!3f0!3m2!1i1024!2i768!4f13.1!5e0!3m2!1sen!2sus!4v1404174824082]