<blockquote>While it is easy to overlook the railroads in Chicago nowadays, this city has been a major rail hub if not the most important railroad city in the nation and the world for more than 150 years. As with any road — rail or otherwise — to be useful for Chicago it must invariably cross the Chicago River. Chicago’s first railroad — the Galena &amp; Chicago Union G&amp;CU, founded in 1848 — was responsible for the city’s first depot and first railroad bridge. The growing city divided by the busy waterway would make the drawbridge a necessity, and the swing bridge, now nearly forgotten, was for decades the most common type of bridge crossing the Chicago River.</blockquote>
via <a href="http://forgottenchicago.com/features/railroads-and-chicago-swing-bridges/">Railroads and Chicago Swing Bridges | Forgotten Chicago | History, Architecture, and Infrastructure</a>.