But its history and grounds have been meticulously preserved, down to the dykes that controlled the flow of water into its expansive rice fields.

Little is known about Jim Robinson, however, including how or when he came to Friendfield, as the property is still called. But records show he was born about 1850 and lived, at least until the Civil War, as a slave. His family believes he worked at Friendfield all his life and was buried there in an unmarked grave.

Until she reconnected with relatives here in January 2008 on a campaign trip, Michelle Obama did not know much about her ancestry or even that Friendfield existed. As she was growing up in Chicago, her parents did not talk about the family's history, and the young Michelle didn't ask many questions.

Her family history - from slavery to Reconstruction to the Great Migration north - connects her to the essence of the African-American experience. Most Sunday evenings during her childhood, Mrs Obama and her parents, Marian and Fraser Robinson III, visited her grandparents at their house nearby.

Fraser Robinson III was born in Chicago and later worked for the city, tending the boilers at a water-filtration plant. But Mrs Obama's grandfather, Fraser Robinson jnr, often reminisced about his childhood in South Carolina. As a little girl, she listened and tried to read between the lines.

Her grandfather's trek north to Chicago was one that millions of southern blacks took over several generations, altering the racial landscape on both sides of the Mason-Dixon Line. But the move did not deliver on its promise. Robinson landed a dull but reliable job with the postal service.

By the time Mrs Obama's parents were married, Robinson and his wife, LaVaughn, were living in an apartment in a public housing project - a tidy complex, as the first lady remembers it, but humble compared with the house that her grandfather's father, Fraser snr, built in South Carolina.

"He was a very proud man. He was proud of his lineage," Mrs Obama recalls of her grandfather. However, she says, "There was a discontent about him."

No one in the family was surprised when Robinson and LaVaughn moved to Georgetown after they retired.

From the age of 10, Mrs Obama was a regular visitor to Georgetown. She remembers the crickets that kept her awake at night and the fresh venison that made her ill. She passed countless times by the Friendfield gate but never noticed the dirt road, much less where it led. For a family that otherwise loved to engage, "we didn't talk about that", she says.

An hour north-east of Charleston in the Low Country region, Georgetown County was settled in early colonial days. By the mid-1800s, thousands of slaves worked its snake- and mosquito-infested riverfront fields, producing half of the rice consumed in the US.

One worker at Friendfield is believed to have been Jim Robinson. He is recorded in the 1880 census as an illiterate farmhand living near the plantation's white owners. He was married with a three-year-old son, Gabriel. Mrs Obama's great-grandfather, Fraser Robinson snr, was born in 1884.

Gabriel Robinson's daughter, Carrie Nelson, now 80, is the oldest-living Robinson and the keeper of family lore.

Seated in an easy chair in the living room of her small ranch-style house, she relies on a tattered family Bible and a long and lively memory to reconstruct the final days at Friendfield and recalls stories her father told her as a girl.

When Gabriel and Fraser Robinson were young, their mother died and Jim remarried. When Fraser was about 10, Ms Nelson recounts, he ventured into the woods to collect firewood, and "a little sapling fell on his arm and it broke." His stepmother brushed off the injury. But the wound became infected, and his left arm had to be amputated.

A witness to the tumultuous family scene was a white man named Francis Nesmith, the son of an overseer at another plantation and a regular visitor to Friendfield.

As Gabriel Robinson told his daughter, Fraser would tag along with Nesmith, and Nesmith grew fond of the one-armed boy. Aware of Fraser's difficult home life, Nesmith asked Jim Robinson if the boy could live with him.

"He said he would take good care of him, and he did," Ms Nelson says. "Uncle Fraser and that man's children grew up together."

In the 1900 census, Fraser is listed as a "house boy" living with the Nesmith family. At 16, he could not read or write but the Nesmith children attended school, and their parents were literate. That left an impression on her uncle, Ms Nelson says.

"They pushed their kids hard into education, and one day Uncle Fraser would, too, because that's what he learned from them," she says of the Nesmiths.

Keenly aware of his wife's heritage, President Barack Obama has called his wife "the most quintessentially American woman I know". During his speech on race in Philadelphia last year, he noted: "I am married to a black American who carries within her the blood of slaves and slave owners."

Jim Robinson's sons prospered. Gabriel joined a turpentine crew and bought a farm west of Friendfield, a portion of which remains in the family. Fraser married Rosella Cohen, taught himself to read and worked as a shoemaker and a newspaper salesman as well as holding down a job at a lumber mill.

Dorothy Taylor, 89, who keeps a picture book of President Obama on her coffee table, remembers seeing "Mr Fraser Robinson" selling the local paper on a downtown street corner. All the students at Howard School, the county's only black high school, knew he took spare copies home each night so his children could read them.

"It was the belief that education was our salvation - education and religion," Ms Taylor says. "You've got to trust in God and learn all you can. Because we had meagre lives. We had nothing."

Mrs Obama's grandfather was born in 1912. He was a standout student and was known as an orator, but at 18, census records show, he was living at home with his parents and working at a local sawmill. It was a time when Georgetown blacks were losing the legal rights and social status they had started to gain after emancipation, and the local economy was in a shambles.

"There were no jobs here," says Harolyn Siau, a Robinson cousin and retired teacher. "I guess a man who thought like he thought, he wouldn't want to do ordinary stuff." Fraser Robinson jnr decided to follow a family friend who had moved to Chicago.

When the Obama campaign began compiling the Robinson genealogy, aides had no idea what they might find. And Mrs Obama knows very little about her other grandparents, although she was told LaVaughn was the granddaughter of a Mississippi preacher.

At least three sons of Fraser snr - Mrs Obama's great-uncles - joined the military. A daughter moved to Princeton, New Jersey, where she worked as a maid, and she cooked southern-style meals for Michelle and her brother, Craig, when they attended Princeton University.

An uncle of Mrs Obama, Thomas Robinson, served for 25 years as the beloved principal of an elementary school in an African-American community that had formed near the Friendfield property line.

"It makes more sense to me," Ms Obama says.

"If the patriarch in our lineage was Fraser, a shoemaker with one arm, an entrepreneur, someone who was able to own property, and with sheer effort and determination was able to build a life in this town - that must have been the messages that my grandfather got."