Bridges

"The Chicago River:  The river with its branches gives to the city a water frontage of 58 miles, to which Lake Michigan adds 22 more.   It divides the city into three distinct parts, known as the North, South, and West divisions.   Communication between these divisions is afforded by half a hundred bridges which span the river at almost every street.   These bridges are swung on a central pivot by electricity and can be moved very quickly.  The electric and cable cars  pass through tunnels under the river."
From the back of the Rush Street Bridge postcard, 1907.