The Hannibal & St. Joseph Railroad operated from 1846-1883, the first railroad to cross Missouri. It is said to have carried the first letter to the Pony Express on April 3, 1860. The line connected the second and third largest cities in Missouri prior to the Civil War. The line suffers periodic attacks by pro-Confederate bushwhackers, but it remains active throughout the Civil War and, in 1867 with the construction of the Hannibal Bridge, turns Kansas City into an important western railroad hub on the cattle trade between Chicago and Texas. The first assignment of Col. Ulysses S. Grant during the American Civil War was protecting the railroad and Pony Express mail. Grant was promoted to brigadier general in August 1861 after the assignment. Shortly after Grant left his assignment, the railroad experienced its worst disaster of the war on September 3, 1861, when bushwhackers burned a bridge over the Platte River, causing a derailment that killed between 17 and 20 and injured 100 in the Platte Bridge Railroad Tragedy. The disaster sparked further violence that culminated in the near-destruction of Platte City.