Jefferson Barracks was established in 1826 because of its close proximity to the Mississippi River, whose 2,320-mile course from Lake Itasca, Minnesota to the Gulf of Mexico made it a vital lifeline for moving people, supplies, and raw materials, growing the City of St. Louis and helping propel western expansion. During the golden age of steamboats from 1830-1850, St. Louis's cobblestone levee commonly received more than 150 steamboats at one time as cotton, timber, food, and coal moved to market, and the city's growth brought new churches, a public school system, and a water system, even though fire destroyed 15 city blocks and 23 steamboats at the riverfront in 1849 and a cholera epidemic that same year claimed thousands of lives. By the 1850's, St. Louis was the second largest port in the country. During the Civil War, blockades were set up along the river, including at Jefferson Barracks, where artillery was positioned to control river traffic after U.S. Federal Intelligence learned that Confederates sought to target the Arsenal, Jefferson Barracks, the railroads, and the river traffic. In modern commerce, barge transportation from St. Louis reaches a population of 90 million people and 29 industrial centers, with a single barge carrying as much cargo as 15 rail cars or 60 semi trailer trucks, and towboats moving freight with greater fuel efficiency than locomotives or trucks. More than 60% of U.S. grain exports move by barge, along with coal and other fuels, and the barge industry generates 124,000 direct jobs, $10 billion in freight revenue, and $300 million and $55 million in federal and state revenue respectively. The Jefferson Barracks Bridge, also known as the J.B. Bridge, is a pair of 909-foot-long steel arch bridges carrying Interstate 255 and U.S. Highway 50 across the Mississippi on the south side of St. Louis, with the north span opened in 1983 and the south span in 1992, replacing a steel truss bridge built in 1941. Jefferson Barracks, named for President Thomas Jefferson, was deactivated in 1946 after becoming in a few short years the largest military post in the United States, a centrally located outfitting and training center for the military effort of the entire western half of the United States whose roles included base camp for troops fighting the Indian Wars, ordnance depot, engineer base, cavalry post, general hospital, induction and separation center, and basic training center. Its historic district includes military buildings and related sites dating from the 1850s through the post-World War II years, including the Old Ordnance Room Museum, the Powder Magazine Museum, and the Laborers House and Ordnance Stable, all listed on the National Register of Historic Places. Among the notable figures who served there were Stephan W. Kearny, Zackary Taylor, Jefferson Davis, Robert E. Lee, Ulysses S. Grant, William T. Sherman, and Phillip Sheridan. The surrounding landscape also reflects the river's long influence through the Mississippi Flyway, a migration route between central Canada and the Gulf of Mexico used by many birds, and through local prairie, forest, riparian woods, wildlife, and karst geology with caves, springs, sinkholes, and lost streams; limestone quarried along the Mississippi River bluffs was used for many of the original Jefferson Barracks structures.