In 1821, William Becknell put a notice in the "Missouri Intelligencer," announcing that he was organizing a party to go "westward, for the purpose of trading for horses and mules and catching wild animals of every description." On September 1, 1821, his party crossed the Missouri River at Arrow Rock and set out along what would become known in a few years as the Santa Fe Trail. There had long been trade along this way: years before the US acquired the Louisiana Purchase, the Chouteau family of St. Louis had been granted a fur trading monopoly with the Spanish at Santa Fe.