George Brown Tindall and David E. Shi, America: A Narrative History, 6th ed. (New York: W. W. Norton & Company, 2004), 605.
Escapees often made it out on their own – [Fredrick] Douglass borrowed a pass from a free black seaman – but many were aided by the Underground Railroad, which grew into a vast system to conceal runaways and spirit them to freedom, often over the Canadian border. Levi Coffin, a North Carolina Quaker who moved to Cincinnati and did help many fugitives, was the reputed president. Actually, there seems to have been more spontaneity than system about the matter, and blacks contributed more than was credited in the legend. A few intrepid refugees actually ventured back into slave states to organize escapes. Harriet Tubman, the most celebrated, went back nineteen times.