Secret system in northern U.S. states to help escaping slaves. Its name derived from the need for secrecy and the railway terms used in the conduct of the system. Various routes in 14 states, called lines, provided safe stopping places (stations) for the leaders (conductors) and their charges (packages) while fleeing north, sometimes to Canada. The system developed in defiance of the Fugitive Slave Acts and was active mainly from 1830 to 1860. An estimated 40,000 to 100,000 slaves used the network. Assistance was provided mainly by free blacks, including Harriet Tubman, and philanthropists, church leaders, and abolitionists. Its existence aroused support for the antislavery cause and convinced Southerners that the North would never allow slavery to remain unchallenged.