2½ miles North-East of Stromness, Mainland, Orkney, Scotland.
Unstan, also referred to as the Knowe of Unstan, is a well preserved example of a chambered cairn situated on a small peninsular protruding into the southern end of the Loch of Stenness. Two miles away at the northern and eastern ends of this brackish Loch is the Heart of Neolithic Orkney World Heritage site, encompassing a number of exceptionally important structures, including the Stones of Stenness, the Ring of Brodgar, the Ness of Brodgar, Maeshowe, and the Barnhouse.
Probably built between 3,400 and 2,800 BC, Unstan is difficult to classify as it is a blend of two distinct styles of construction; its 43 feet diameter stone mound is very much of the Maeshowe-type, but the chamber within is in the Orkney-Cromarty style. When Robert Stewart Clouston excavated it in July 1884, it had the external appearance of a simple grassy mound with a notable depression at the top where the roofing stones had either given way or been robbed. Excepting the depression it retains much the same form today, with a layer of turf over a concrete dome which was added in the 1930's to protect the cairn from the elements.
The remarkably intact entrance passage faces very slightly North of East and extends 11 feet into the interior; due to its low height it is best tackled on hands and knees. The chamber beyond is aligned on an almost North to South axis, and is broadly barrel-shaped at 21 feet long and between 4 and 6 feet wide. Four equidistant pairs of flanking uprights divide it into five compartments; the centre one has a small side compartment, just 3½ high, inside the western face. The extreme ends of this and the main chamber each have stone slabs set into the walls. Between the uprights leading into the northern and southern-most compartments is a low stone, much like a step, with further stones laid in the floor of the latter to divide it into two.
As one would expect the chamber contained fragments of human and animal bone, the majority of which was in compartment 2, but the side compartment (6 on the plan) contained two crouched skeletons; an unusual arrangement for the Neolithic which lends weight to the theory that the cairn was also used by later peoples. There is more evidence of such use, or misuse; a barbed arrowhead reminiscent of the Beaker People was found in the entrance passage; the western upright between compartments 4 and 5 is covered in the carved graffiti of 19th Century visitors; and there are runic inscriptions on some of the wall stones as well as the lintel above the entrance of 6, but these are generally thought to be later fakes rather than an indication of a Maeshowe-like visitation by Vikings.
Unstan's real claim to fame, however, is its extensive collection of pottery, with the apparently deliberately broken remains of between 20 and 30 bowls, all of which had seen much use before being committed. These generally take the form of a shallow bowl with a decorative band of alternating, angled grooves set around the circumference of the rim (see here), and as these were the first examples to be found of an artistic style which was prevalent across Orkney at this time, they came to be known as Unstan Ware. The patterning clearly had some wider significance as angled stonework was used to dress the outer faces of several cairns; Blackhammer on Rousay being one of the more elaborate.
Archaeology Data Service - Excavation Report