The discovery of the cairn

Like so many of Orkney's other prehistoric monuments, the discovery of the Isbister chambered cairn - best known today as the Tomb of the Eagles - was purely accidental.

The cairn was uncovered by a local farmer, Ronald Simison, on his land on the south-eastern tip of the island of South Ronaldsay in 1958.

After noticing flagstones jutting from a mound in a field, Mr Simison began digging and was astounded when, ten minutes later, he reached the bottom of what looked like a wall.

Excited by his discovery, he continued and, before long, had uncovered a black and white polished mace head, axe heads and a tiny jet button.

Spurred on by his unexpected discoveries, he dug further until he reached the top lintel of what he recognised as being an entrance of some sort.

Mr Simison continued exposing the newly discovered entrance bit by bit and was eventually able to peer into the darkness of the small stone cairn.

There, by the flickering light of a cigarette lighter, Ronald Simison saw the 30 human skulls that filled the chamber - his first encounter with the long-dead occupants of the Tomb of the Eagles.

However, shortly after this discovery the tomb was sealed up again, pending a thorough archaeological excavation. But this promised excavation was a long time in coming.

More than 20 years passed - years in which Mr Simison tried in vain to persuade the authorities to investigate the Isbister tomb.

Eventually he gave up and decided to do the job himself.

The results of the excavation