History textbooks and popular media generally depict the Underground Railroad as an arduous overland journey, one that would stretch for days until the right covered wagon allowed the enslaved to cross over into a free state. But while this was the case for many enslaved people living in border states, for those farther from the Mason-Dixon Line, escaping by land was almost unattainable.

Instead, as scholars in recent years increasingly are documenting, the method for abducting the enslaved from Africa became the same method that would help many regain their freedom: travel by boat.

“Most maps would lead you to believe that people were escaping over land by foot or by horse or by wagon from the Deep South, but the historical record doesn’t back that up at all,” said Timothy Walker, a professor of history at the University of Massachusetts at Dartmouth and editor of the book “Sailing to Freedom: Maritime Dimensions of the Underground Railroad.”

Escaping to a border state more than a couple of days’ walk away was impractical, Walker said, and the most that anyone could travel was 20 miles in one night. “Without a proper pass or permission to go a very long distance through the Deep South, you risk being stopped and challenged and recaptured,” he said.

It’s hard to know how many enslaved people escaped by sea, Walker said, since the people fleeing rarely left a paper trail. But some estimates say that as many as 100,000 people escaped U.S. enslavement by various methods. Abolitionist William Still kept a record of the people he helped, and his book “The Underground Railroad” details many arriving to freedom by boat.

In the early 1800s, shipyards in Alexandria, Norfolk, Charleston and as far south as coastal Florida became hotbeds of escape — and rumors.

Ships departing such ports, including those headed north to cities such as New Bedford, Mass., were often manned by enslaved people who knew the waterways well. Enslaved Black people had worked in the maritime industry as early as the Revolutionary War, and for parts of the 19th century, they worked on most fishing boats and merchant vessels and in shipyards.

Their enslavers sometimes loaned them to work for pay under Quakers, who generally opposed slavery, and free Black men, said Lee Blake, president of the New Bedford Historical Society.

On sea voyages, some sympathetic captains and crews stowed away enslaved people and helped them reach a free state.

“They can escape very quickly by water, because a ship that is sailing 24 hours a day up the Gulf Stream can travel 200 miles in a day,” Walker said. “So a ship passage is relatively quick, relatively safe, and you’re not in danger of being recaptured when you’re at sea.”

Accordingly, he said, some formerly enslaved men sought safety back at sea on whaling voyages lasting two to three years at a time.

One notable maritime escape occurred in 1796 in Philadelphia, then the nation’s capital, where a news bulletin called for information about “a mulatto woman named Ona Judge” enslaved by President George Washington. Though Pennsylvania had passed a “gradual abolition” act in 1780, Washington brought Judge back-and-forth between Philadelphia and his estate at Mount Vernon in Virginia. Before one return trip to Virginia, Judge boarded a ship and fled — “without provocation,” the bulletin said.

But the risks for maritime escapes were manifest. A 1793 law — a precursor to the Fugitive Slave Act of 1850 — prohibited aiding anyone who escaped by boat. Bounty hunters waited for ships at port cities, and anyone caught abetting a fugitive could have their boats confiscated or be imprisoned.

The latter was the fate for the crew of the Pearl Schooner. The ship was trying to escape from Washington, D.C., to New Jersey in 1848 with 77 enslaved men, women and children. But when the Pearl Schooner was stopped amid difficult water conditions at the mouth of the Potomac River by the Chesapeake Bay near Maryland’s Point Lookout, enslavers and other armed volunteers overtook the ship by threat of force. The enslaved were sold to plantations in the Deep South.

So crews and enslaved people alike went to great lengths to hide their plots. (Judge, for instance, said she didn’t reveal the name of the captain who helped her escape until after he died, “lest they should punish him for bringing me away.”)

In Norfolk, which saw heavy port traffic, fugitive-smuggling journeys typically began at the docks’ dirty loading areas in the middle of the night, Cassandra Newby-Alexander, a contributor to Walker’s “Sailing to Freedom” volume, explained in a panel discussion for the Library of Congress. Women “were rare at the docks, so they’d wear men’s clothing to gain access,” said Newby-Alexander, who directs the Joseph Jenkins Roberts Center for the Study of the African Diaspora at Norfolk State University.

“On some schooners, captains built secret compartments so that more than one or two people could escape,” she said. One captain in Norfolk, James Watson Fountain, “had a secret compartment so large that over 20 people could cram in.” On passenger ships, a crewman would smuggle people into a compartment near the boiler room; such journeys could last up to three days.

Early on, Massachusetts was a welcoming place to land, having been the first state to abolish slavery altogether in 1784. New Bedford was called the “Fugitive’s Gibraltar,” Blake said, a place where the formerly enslaved could find not only refuge but employment and wealth. So many Black people fled to New Bedford that by 1853 almost 30 percent of its residents said they had been born in the South.

Abolitionists in New Bedford such as Nathan and Mary Johnson often housed transient people and, through their work and social affairs, enticed wealthy White friends to help pay for escapees’ freedom.

Residents had a system, too, for when suspected bounty hunters pulled into port, Blake said: Someone would ring a bell, and a group would form a blockade or help the escaped people get a head start in hiding. If the suspected bounty hunters persisted, “the locals beat them up,” Blake said, and kicked them out.

The same local solidarity played out in nearby Nantucket in the early 19th century. Arthur Cooper and his wife and children had fled from Alexandria, Va., to New Bedford on the sloop Regulator and settled in Nantucket. In 1822, a slave catcher named Camillus Griffith attempted to invoke the Fugitive Act to take the Coopers back south. When threats and intimidation didn’t work, Griffith reached out to local law enforcement for help, arguing that they had to follow the law.

But Nantucket residents physically blocked Griffith long enough for a magistrate to refuse to enforce the act and force him to leave the city. According to Griffith’s account, that magistrate, Alfred Folger, “observed to me that the laws of their state did not recognize any persons as slaves, and if I attempt to molest these people or remove them, he should consider it his duty as a magistrate to arrest me and my party.”

The maritime Underground Railroad’s legacy today is honored in cities such as Norfolk and New Bedford, whose whaling museum hosts a “Sailing to Freedom” exhibit expanding on Walker’s book.

That exhibit features Ona Judge, whom George Washington had once enslaved. Despite Washington’s efforts to reclaim her, she lived out her days in New Hampshire — thanks in part, as with thousands of others, to brave Black deckhands.

“I am free,” Judge told an interviewer late in life, “and have, I trust, been made a child of God by the means.”