The early history of New Orleans was one of uninterrupted growth. In the 1850 census, New Orleans ranked as the 6th largest city in the United States, with a population reported as 168,675. It was the only city in the South with over 100,000 people. By 1840 New Orleans had the largest slave market in the nation, which contributed greatly to its wealth. During the antebellum years, two-thirds of the more than one million slaves who moved from the Upper South in forced migration to the Deep South were taken in the slave trade. Estimates are that the slaves generated an ancillary economy valued at 13.5 percent of the price per person, generating tens of billions of dollars through the years.