Chicago's geography has presented unusual requirements since the earliest days of the city. A narrow river, with low banks, rans through the heart of the city, requiring frequent crossings. Yet the navigable river was one of the world's great ports, and the low bridges over the river had to accommodate the frequent passage of masted ships in the 1800s.

Chicago River by Paul Sager, on Flickr


The first ferry service to cross the river was established in 1829, where the Lake Street Bridge is now. In 1833 a floating bridge of logs was in operation just north of the present Randolph Street Bridge. A foot bridge over the north branch was built in 1832 at Kinzie Street.

Chicago River Lake Street Bridge


The first drawbridge was constructed in 1834, but its approaches impeded navigation and it was torn down in 1839. The South Siders had hoped to keep trade on their side of the river, but a new floating bridge was built in 1840, and three more soon followed. All these floating bridges were swept away in a sudden spring flood in 1849, and the bridge design and building process started again.

Chicago River view


The first municipally-funded bridge opened in 1857. By 1871, the city had 27 movable bridges. Most of these were swing bridges, which turned on a center pier to swing out of the way of ships. The narrow channel saw frequent collisions between sailing ships and bridges, spurring the search for other solutions.

Chicago River view


A jackknife bridge was introduced in the early 1890s, but the style was not embraced by the city. Two other styles, the vertical lift bridge and the Scherzer rolling lift bridge, were developed in the mid-1890s. Both can still be found in the city. A vertical lift bridge is pulled up and down from counterweights in two tall towers on either side of it.

Canal Street Railroad Bridge


Frequent bridge openings vexed the city, making the North and West Sides less desirable. Tunnels built at Washington Street (1869) and LaSalle Street (1871) proved extremely useful for cable cars, which could not cross an openable bridge

Canal Street railroad bridge


Until 1872 the swing bridges were turned by hand, but then steam power was installed on the Dearborn Street Bridge and shortly most all the other downtown bridges were steam operated.

Chicago River view


The bridge most identified with Chicago, the trunnion bascule, was developed in 1900, and the first one built, opened in 1902, remains at Cortland Street. The bridge's leaves are suspended on axles (trunnions), with the counterweights in a riverbank pit. The new design proved efficient to operate and allowed trusses to be set at banister height and eventually moved underneath the road deck.

Chicago River Bridge Lift


What made the trunnion bascule bridges so unique to Chicago and so necessary to perfect? In 1830, right around the time of the first movable bridge design, the city’s population was about 4,000. By 1857, when the swing bridge was being introduced, the population had grown to 90,000. Bascule bridges were the most practical for these large and growing numbers of people and remain common today.

Chicago River Bridge


Translated from French, “trunnion” means “pivot point” and “bascule” means “seesaw.” Also known as the “Chicago Style,” the bridge's leaves are suspended on axles (trunnions), with massive concrete counterweights located below the bridge, in the riverbank pit. There are single-leaf bascule bridges, which were constructed where the river was not very wide and often used for trains, and double-leaf bascule bridges, which could be compared to two seesaws across from each other.

Chicago River Bridge Lift


Some of the bridges still used downtown are double decker, with vehicle traffic on the bottom level and L trains passing through on the upper level. Two bridges — at Jackson Boulevard and Lake Street — are now over 100 years old.

Chicago River Bridge Lift


Images in this post all use Canon L-series lenses, most of the EF variety on digital and film EOS bodies, some with older FD manual focus versions mounted to a Sony mirrorless body. Details of the cameras and lenses can be accessed from the host Flickr pages via the URL links of each title.

Chicago River Bridge Lift