The excavation of the cairn

Built around 3,000 BC, the Tomb of the Eagles was in constant use for around a century.

Excavations revealed that the cairn was not built in one go, but around 150 years after the first stage of construction, and over the space of around 200 years, the tomb was gradually enlarged.

Consisting of a long, rectangular main chamber, 3.5 metres high, the Isbister cairn is a fine example of a hybrid tomb - containing the stalled compartments of the Orkney-Cromarty cairns and also incorporating three side-cells of the Maeshowe style.

Isbister was divided into three stalls by upright flagstone slabs built into the walls. Originally, it had two low compartments at either end of the main chamber, each with a stone shelf across. By the time of the excavation, however, only one of the shelved chambers remained, and this was found to be full of human bones.

Beneath this surviving side chamber was a foundation deposit made up of a mixture of bones from around 15 humans as well as the remains of the white-tailed sea-eagle.

The eagle remains intrigued the excavators, who had also found large numbers of sea-eagle bones littered throughout the tomb. This led to the idea that the bird was somehow significant to the people who built, and used, the tomb.

Human remains lay throughout the tomb but, as is typical in the Neolithic chambered tombs, these were not complete skeletons but a selection of bones that had been mixed together into a communal "bone pile" before being laid out in the tomb.

In total, over 16,000 assorted bones were found inside the Isbister cairn - remains that had belonged to at least 342 individuals. Human skulls lined the walls and beside each skull was a pile of other bones. The two cells at the western end of the main chamber held dozens more skulls, along with an assortment of other human remains.

However, the shelved compartment to the to the south was markedly different. It contained a number of human bones but there was no trace of any skulls.

As well as the human and eagle bones, the Isbister excavation recovered huge quantities of animal and fish bone. Lamb remains in particular were thought to be the result of joints of meat and their discovery may offer a vague hint at one of the ceremonies undertaken inside the chamber.

Outside, large numbers of animal remains within the hornwork seemed to indicate that the sacrifice of animals, particularly calves, was commonplace.

The young animals appeared to have been led to the tomb and slaughtered before being dismembered, the meat left lying. The fact that the calf remains were left outside the tomb, while the lambs were found inside, added weight to the idea that Orkney's chambered cairns were not merely repositories for the dead but actually used for other specific ceremonies throughout the year.

Opposite the opening of the tomb's long entrance tunnel lay a mound of broken pottery.

Weighing in at around 26 kg, the pottery shards came from an estimated 46 different pots - pots that had seemingly been deliberately broken outside the structure.

The smashed pots were burned before the charred fragments were carried into the cairn, where they were deposited in the main chamber.

What was the Significance of the Eagle?