“The story of slavery in New England is like a landscape that you learn to see,” said Anne Farrow, who co-wrote “Complicity: How the North Promoted, Prolonged, and Profited From Slavery” and who is researching a new book about slavery and memory. “Once you begin to see these great seaports and these great historic houses, everywhere you look, you can follow it back to the agricultural trade of the West Indies, to the trade of bodies in Africa, to the unpaid labor of black people.”

As the nation prepares to mark the 150th anniversary of the American Civil War in 2011, with commemorations that reinforce the North/South divide, researchers are offering uncomfortable answers to that question, unearthing more and more of the hidden stories of New England slavery — its brutality, its staying power, and its silent presence in the very places that have become synonymous with freedom. With the markers of slavery forgotten even as they lurk beneath our feet — from graveyards to historic homes, from Lexington and Concord to the halls of Harvard University — historians say it is time to radically rewrite America’s slavery story to include its buried history in New England.

we had a little slavery, early on. But it wasn’t real slavery. We never had many slaves, and the ones we did have were practically family. We let them marry, we taught them to read, and soon enough, we freed them. New England is the home of abolitionists and underground railroads. In the story of slavery — and by extension, the story of race and racism in modern-day America — we’re the heroes. Aren’t we?

When it comes to slavery, the story that New England has long told itself goes like this: Slavery happened in the South, and it ended thanks to the North. Maybe

It sounds like a classic account of Southern slavery. But Codman’s body didn’t hang in Savannah, Ga.; it hung in present-day Somerville, Mass. And the reason we know just how long Mark the slave was left on view is that Paul Revere passed it on his midnight ride. In a fleeting mention from Revere’s account, the horseman described galloping past “Charlestown Neck, and got nearly opposite where Mark was hung in chains.”

In the year 1755, a black slave named Mark Codman plotted to kill his abusive master. A God-fearing man, Codman had resolved to use poison, reasoning that if he could kill without shedding blood, it would be no sin. Arsenic in hand, he and two female slaves poisoned the tea and porridge of John Codman repeatedly. The plan worked — but like so many stories of slave rebellion, this one ended in brutal death for the slaves as well. After a trial by jury, Mark Codman was hanged, tarred, and then suspended in a metal gibbet on the main road to town, where his body remained for more than 20 years.

It was the 1991 discovery of an African burial ground in New York City that first revived the study of Northern slavery. Since then, fueled by educators, preservationists, and others, momentum has been building to recognize histories hidden in plain sight. Last year, Connecticut became the first New England state to formally apologize for slavery. In classrooms across the country, popularity has soared for educational programs on New England slavery designed at Brown University. In February, Emory University will hold a major conference on the role slavery’s profits played in establishing American colleges and universities, including in New England. And in Brookline, Mass., a program called Hidden Brookline is designing a virtual walking tour to illuminate its little-known slavery history: At one time, nearly half the town’s land was held by slave owners.

“What people need to understand is that, here in the North, while there were not the large plantations of the South or the Caribbean islands, there were families who owned slaves,” said Stephen Bressler, director of Brookline’s Human Relations-Youth Resources Commission. “There were businesses actively involved in the slave trade, either directly in the importation or selling of slaves on our shores, or in the shipbuilding, insurance, manufacturing of shackles, processing of sugar into rum, and so on. Slavery was a major stimulus to the Northern economy.”

Turning over the stones to find those histories isn’t just a matter of correcting the record, he and others say. It’s crucial to our understanding of the New England we live in now.

“The absolute amnesia about slavery here on the one hand, and the gradualness of slavery ending on the other, work together to make race a very distinctive thing in New England,” said Joanne Pope Melish, who teaches history at the University of Kentucky and wrote the book “Disowning Slavery: Gradual Emancipation and ‘Race’ in New England, 1780-1860.” “If you have obliterated the historical memory of actual slavery — because we’re the free states, right? — that makes it possible to turn around and look at a population that is disproportionately poor and say, it must be their own inferiority. That is where New England’s particular brand of racism comes from.”