The largest mausoleum measured 15,000 square feet, said Dr Roland-Pierre Gayraud, who has been excavating in the Qarafa al-Kubra district of Cairo for 11 years. "All the roads around the mausoleum were paved with stone, there were numerous gardens, a carefully maintained water system and we have found a number of decorative stuccos," he said. Pillaged in the 12th Century, stripped by fertiliser sellers in the early 20th Century and now buried under Cairo's urban sprawl, the site had never previously been studied.

 The Fatimids, who claimed descent from Fatima, the daughter of Mohammed, were a dynasty both revolutionary and imperial. Their reign lasted from 909 to 1171, during which time they extended their empire from Morocco to the Red Sea. They were the founders of Cairo and the ancestors of the Aga Khans.

 In the mausoleum, several bodies were found in elaborate "tiraz", fabrics reserved only for the caliphs, who could give them as gifts to favoured subjects. One man with a beard dyed red with henna - a mark of honour still found in Saudi Arabia - was found wrapped in three tiraz. Mysteries surrounded many of the remains. In one tomb, 17 women were buried along with foetuses. A pot found elsewhere contained goat vertebrae and piles of hair.

 The ruling caliphs of the Fatimids took the title Divinely Guided One, and they maintained a vast network of agents whose task was to subvert the existing Sunni order and the regimes that supported it. They also favoured learning and, at the height of their power, collected in Cairo a royal library consisting of more than 100,000 manuscripts elegantly transcribed and splendidly bound.

 Their downfall began with the reign of the mad caliph al-Hakim (who reigned from 996-1021), who proclaimed himself God and provoked a series of struggles that lead to the overthrow of the caliphate.