Freedom suits are legal petitions filed by slaves for freedom.Hundreds of such suits were filed in the United States and its territories before the American Civil War, including during the colonial period. Most were filed during the nineteenth century. After the American Revolution, most northern states had abolished slavery, and the United States Congress prohibited it in some newly established territories. Slave states and territories had slave laws that created ""just subjection."" They also had laws that provided for slaves to sue on the basis of ""wrongful enslavement.""Free states and territories generally held that slaveholders forfeited their rights to ""property"" by bringing slaves into the state for extended travel or residency. As people began migrating and traveling more frequently, residency changes provided grounds for some slaves to sue for freedom. Courts in Missouri, Kentucky, Louisiana and Mississippi freed numerous slaves on the grounds of their having been held illegally in free states. Other grounds were that the person was freeborn and illegally held in slavery, or that the person was illegally held because of having been descended from a freeborn woman in the maternal line under the partus sequitur ventrem doctrine. Even manumitted slaves could find need to sue for freedom.By 1846, several hundred such cases had been tried in state courts across the country. Slaves had gained freedom in 57 percent of the 575 freedom suits decided in state appellate courts. The largest corpus of freedom suits available to researchers today is in St. Louis, Missouri, where 301 files dating from 1814–1860 are among St. Louis Circuit Court Records discovered in the 1990s. Slightly less than half the slaves in these cases gained freedom.The first freedom suit in St. Louis was filed in 1805 by Marguerite Scypion, an African-Natchez woman. Briefly, she filed based on maternal descent from her Natchez grandmother. As the Spanish had ended Indian slavery in 1769, Scypion held that her mother, Marie-Jean Scypion, should have been freed at the time based on her Natchez ancestry, and that Marguerite herself was illegally held as a slave from birth. Having had an earlier ruling in her favor overturned on appeal, in 1826 Marguerite Scypion renewed her suit for freedom, filing against her current master Jean Pierre Chouteau, who headed one of the most prominent fur trading families in the city. She gained freedom for herself and all her mother's descendants in 1836, in a decision upheld by the US Supreme Court.As the city was the ""Gateway to the West"", and Missouri was admitted as a slave state (bordered by free states), the St. Louis courts heard many freedom suits. If the court held there was a basis for the suit, it appointed counsel for slave plaintiffs. Many leading attorneys in St. Louis worked on slave suits. In 1824, the Missouri courts established the precedent known as ""once free, always free"", freeing slaves in Missouri based on their having been held by their masters illegally in free states or territories. This held for decades until 1852 and the Dred Scott v. Sandford decision, which ruled that Scott should have filed for freedom while in a free state.