Meet Marie-Pierre: she claims to be from one of history's most persecuted peoples, the Moors

The story of Marie-Pierre's bloodline is marked with a unique sadness: she belongs to a hidden tribe of pariahs, a tribe that has arguably been the victim of Europe's oldest "Islamophobia".

Marie-Pierre Manet-Beauzac says that she is a descendant of Moorish soldiers.

Sitting in her little house near Tarbes in the French Pyrenees, Marie-Pierre Manet-Beauzac is talking about her ancestry. For most people this would be agreeable, even pleasurable. For the 40-something mother of three Marie-Pierre, the story of her bloodline is marked with a unique sadness: she belongs to a hidden tribe of pariahs, a tribe that has arguably been the victim of Europe's oldest "Islamophobia".

Marie-Pierre is a Cagot. If the word "Cagot" means nothing to you, that is unsurprising. The history of the Cagot people is obscure. Some assert that it has been deliberately erased. Marie-Pierre certainly believes this: "To talk about the Cagots is still a bad thing in the mountains. The French are ashamed of what they did to us, the Cagots are ashamed of what they were. That is why no one these days will confess that they are of Cagot descent."

No one except, uniquely, for Marie-Pierre. She is probably the only person in the world willing to admit she is of Cagot blood. So what is the story of the Cagots? As a people, they are first mentioned in documents around the 13th century. By then, they are already regarded as an inferior caste, the "untouchables" of western France or northern Spain. In medieval times the Cagots - also known as agotes, gahets, capets, caqueux, and many other variants - were divided from the general peasantry in several ways. They had their own urban districts, usually on the wrong side of the river. They were dismal ghettoes known as cagoteries, traces of which can still be found in Pyrennean communities like Campan or Hagetmau.

For hundreds of years, Cagots were treated as different and inferior wherever they went. In the churches, they had to use their own doors (at least 60 Pyrenean churches still boast "Cagot" entrances). Inside the church, they had their own fonts. Daily Cagot life was likewise marked by segregation. Cagots were forbidden to enter most trades or professions. They were forced, in effect, to be the drawers of water and hewers of wood. So they made barrels for wine and coffins for the dead. They became expert carpenters: ironically they built many of the Pyrenean churches from which they were partly excluded.

Some of the other prohibitions on the Cagots were quite bizarre. They were not allowed to walk barefoot, like normal peasants. This gave rise to the legend that they had webbed toes. Cagots could not use the same baths as normal people. They were given the church's holy communion - a small wafer of bread - on a long wooden spoon, to keep them at a distance from the priest delivering the sacrament. Cagots were not allowed to touch the parapets of bridges. They had to wear a goose's foot conspicuously pinned to their clothes to reveal their origins - a chilling precursor of the star of David that the Nazis forced Jews to wear for identification.

The Cagots were not even allowed to eat alongside non-Cagots, a prohibition that gave rise to the legend that the Cagots were cannibals. Marriage between Cagots and non-Cagots was almost impossible. Nonetheless, love affairs across the divide did occur and there are poignant songs from the 16th and 17th centuries lamenting these tragic misalliances. Sometimes the bigotry was brutally enforced. In the early 18th century, when a prosperous Cagot in the Landes region was caught using the font reserved for non-Cagots, his hand was instantly chopped off and nailed to the church door. A Cagot who dared to farm his fields - which was strictly forbidden - had his feet pierced with hot iron spikes. Even in death the discrimination persisted: the Cagots were buried in their own humble cemeteries. One can be seen today in Bentayou-Seree, a tiny village north of Pau.

So where did the Cagots originate? And why did they suffer such bigotry? Their provenance is opaque, partly because the Cagots themselves have disappeared from view. During the French Revolution, the laws against Cagots were formally abandoned and many Cagots took the opportunity to pillage local archives and erase any record of their tainted ancestry. After 1789, they slowly assimilated into the general populace; many of them emigrated.

Nonetheless, there are historical accounts of the Cagots which afford an intriguing glimpse. Contemporary sources describe them as being short, dark and stocky. Confusingly, some others saw them as blonde and blue-eyed. Francisque Michel's Histoire des races maudites (History of the Cursed Races, 1847) was one of the first proper studies of this strange people. He found Cagots had "frizzy brown hair". He also found that at least 10,000 Cagots were still scattered across Gascony and Navarre, still suffering repression nearly 70 years after the cagot caste was "abolished".

Since Michel's pioneering work, various historians have tried to solve the cagot mystery. One common theory is that they were lepers or contagious cretins. This would explain the rules against Cagots touching anything used by non-Cagots. However, this theory falls down on the many descriptions of Cagots being perfectly healthy, even sturdy. Another idea is that the Cagots were slaves of the Goths, who inundated France in the Dark Ages. Hence the name "ca-got", from "cani Gothi" or "dogs of the Goths". But this fails to explain the many variants of the Cagot name, and does not square with the geographical distribution of the Cagots. In fact, the name probably derives from "cack" or "caca", which is a term of abuse in itself.

Last year, the British writer, Graham Robb, offered a new theory. In his book entitled The Discovery of France, Robb suggests that the Cagots were originally a guild of skilled medieval woodworkers; in this light, the bigotry against them was commercial rivalry, which became fossilised and regimented over time. It is a confusing picture. So who is right? Perhaps we should ask an actual Cagot. Marie-Pierre Manet-Beauzac has traced her descent from various communes in the French Pyrenees and believes she is a purebred Cagot. And she has no doubts about the Cagots' background.

"I believe the Cagots are descendants of Moorish soldiers left over from the eighth century Muslim invasion of Spain and France. That's why some people called them 'saracens'. I am quite dark, and my daughter Sylvia is the darkest in her class." This is true, as I can see from Marie-Pierre's children. As for her theory, it is supported by many French experts because it neatly explains the fierce religious disapproval of the Cagots. By this reckoning, the Cagots were converted Muslims (perhaps interbred with Basques - hence their stocky and unusual looks). However, even though they paid homage to Christianity, they were never wholly trusted by the church.

As for their geographical spread, that is explained, as Robb implies, by the Cagots' default profession: they worked with wood, so they went where the business took them, commonly to places associated with the great St James pilgrimage routes - from France, across the Pyrenees into Spain and on to Santiago de Compostela. These were bustling communities that needed lots of stables, houses, and barrels - and cagot carpentry to make them.

Even today, Hagetmau, a town on the Compostela pilgrim route that only demolished its cagoterie ghetto in 2004, is associated closely with woodworking, and a huge wooden chair on the Hagetmau roundabout subconsciously underlines the town's cagot past. Marie-Pierre shows me a website where she is gathering information about Cagot life. She points to a list of villages associated with Cagots. "Some like to say Cagots have disappeared. But this is not true. If you travel near Campan, for instance, you can still see the short, swarthy people descended from the Cagots: the Muslim untouchables."

I ask her if she will let me use a picture of her daughter, Sylvia, and the rest of her children. She shakes her head. "I'm sorry, but no. It is OK for me to admit where I come from. But if people knew about my children's background, it might be difficult for them." She gazes out of the window, at the distant green Pyrenees. "In some places, the hatred still lingers. Even now."