During the 1850s and 1860s, engineers carried out a piecemeal raising of the grade of central Chicago to lift the entire city out of its low-lying swampy ground. Buildings and sidewalks were physically raised on jackscrews. The work was funded by private property owners and public funds, and gave room to build a sewer system that spans most of the city center. The main passages are found in the Loop and surrounding sections, and some parts are now used to house secret speak-easies and rum running routes.

See also: Raising of Chicago