Between 1830 and 1860, more than 3,000 fugitive slaves reached freedom thanks to networks of anti-slavery resistance — commonly known as the underground railroad. Pulitzer Prize-winning historian and Columbia University professor Eric Foner is out with a new book, “Gateway to Freedom: The Hidden History of the Underground Railroad.” The book uses newly discovered, detailed records of slave escapes secretly kept by a leading abolitionist. In his “Record of Fugitives,” Sydney Howard Gay, the editor of the American Anti-Slavery Society’s newspaper, chronicled more than 200 escapes, some of whose stories Foner tells in this sweeping account, listing the identities of escaped slaves, where they came from, who their owners were, how they escaped and who helped them on their way to the North.