{"nrhp_refnum":"06001091","name":"Chain of Rocks Bridge","other_names":[],"category":"structure","location":{"address":"West Chain of Rocks Rd.","address_restricted":false,"city":"Madison","county":"Madison County","state":"IL","lat":38.760463223000045,"lon":-90.17199837941195,"geom_source":"nps_gis"},"listed_date":"2006-12-01","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Transportation","Engineering"],"significance_levels":["national"],"summary":{"what_it_is":"A steel truss highway bridge over 5,350 feet long crossing the Mississippi River between Madison County, Illinois, and St. Louis, Missouri, built in 1927-1929, with a distinctive thirty-degree bend mid-river. The listing includes the bridge and a 1,000-foot section of original roadbed on the Illinois side.","why_significant":"The bridge is significant under Criterion A as a notable link in the US Route 66 corridor, serving as the widest river crossing on the route and an entry to St. Louis. Under Criterion C it is an outstanding example of large-scale 1920s highway bridge engineering, with long cantilevered steel trusses on tapered concrete piers. Its bend, added to ease river navigation, makes it distinctive.","narrative":"Spanning the Mississippi River near its meeting with the Missouri, this steel truss bridge runs more than a mile between Madison County, Illinois, and northern St. Louis. Built from 1927 to 1929 and designed by St. Louis engineer Baxter L. Brown, it is best known for a thirty-degree bend near mid-river, added after boatmen protested and the War Department required a change so the piers would line up with nearby water intake towers. In 1936 it became part of US Route 66, carrying travelers into St. Louis from the north until the late 1960s, when a new Interstate 270 bridge opened upstream. The city of Madison closed the old span in 1968, and it sat idle for years while demolition was considered. A nonprofit group led its conversion to a pedestrian and bicycle path, which opened in 1999. It is valued for its engineering and its role in Route 66 history.","period_of_significance":"1929-1956","architect_builder":"Brown, Baxter L., Engineer; Union Bridge and Construction Company of New York, and the American Bridge Company, Builders","architectural_style":"OTHER: Warrant Truss","criteria":["A","C"],"status_note":"Closed to vehicles in 1968, then repaired and reopened in 1999 as a pedestrian and bicycle bridge; the toll house has been demolished.","vacant_flag":false,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:37.229316-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/53/8913/28891353/content/electronic-records/rg-079/NPS_IL/06001091.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/06001091/cb5521d8d4-800.webp","url_1600":"https://nationalhistoricalregister.com/media/06001091/cb5521d8d4-1600.webp","licence":"CC BY-SA 3.0","author":"Rklawton at English Wikipedia","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Water_Intake_CoRB.JPG\" rel=\"noopener\">Rklawton at English Wikipedia</a>, <a href=\"http://creativecommons.org/licenses/by-sa/3.0/\" rel=\"license noopener\">CC BY-SA 3.0</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Water_Intake_CoRB.JPG"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/28891353","wikipedia":"https://en.wikipedia.org/wiki/Chain_of_Rocks_Bridge","wikidata":"https://www.wikidata.org/wiki/Q592557"},"indexable":true,"url":"https://nationalhistoricalregister.com/illinois/madison-county/chain-of-rocks-bridge-06001091/"}