The cairn was discovered by local farmer, Ronald Simison (Ronnie) in 1958. The discovery, like so many of Orkney's other prehistoric monuments, was purely accidental. Ronnie was looking near the cliff edge for stone to make corner posts for fencing. Weather erosion on a grassy mound revealed horizontal stones. Here Ronnie uncovered a wonderful cache of tools - probably ceremonial - a perfect mace head, 3 small axe heads, including one made of haematite, a knife and a perfect albertite 'button' (all of which are on show in the visitor centre). Intrigued by his find, Ronnie began digging, eventually reaching a dark hole. Using a cigarette lighter, he revealed a chamber containing approximately 30 human skulls - his first encounter with his 5000 year old ancestors. Soon after its discovery, the cairn was sealed up again, awaiting a thorough archaeological excavation within 2 to 3 years. In 1976, almost 20 years later, circumstances enabled Ronnie to undertake the excavation himself. Isbister Chambered Cairn is estimated to have been built around 3000 BC, and used for approximately 800 years. It is 3.5 metres high and consists of a rectangular main chamber, divided into stalls and side cells. It was believed the human remains belonged to around 340 individuals. No complete skeleton was found suggesting that the bodies had been excarnated - left outside until the bones were clean. Recent research questions both the excarnation idea and number of people in the tomb. Once inside the Tomb, at some point the skulls were laid in side chambers and the other bones set in the two end cells. 70 talons from the white-tailed sea eagle and the remains of at least 14 birds were found inside the tomb - the inspiration for the tomb's popular name - The Tomb of the Eagles. Found alongside the human remains, it is believed these magnificent birds, once common in Orkney, were perhaps a totem of the people who built the tomb. The interpretation at the visitor centre includes information about diet, health and the social and spiritual structure of the group who lived in the area 5000 years ago.