Long horned cairn.
|Notes:||Aligned ESE to WNW, the Knowe of Lairo stands on the edge of a hill terrace beneath the Knowes of Ramsay and Yarso. It was excavated in 1936 by Walter Grant and David Wilson.|
Roughly trapezoidal in shape, the cairn is approximately 45.7m in length and is widest (c17m) and highest (c3.2m) at the eastern end. From here it narrows to c9m at the western end, where it stands 1.5m high.
Compared to the size of the cairn, the area covered by the chamber is small. What it lacks in area it makes up for in height, the roof reaching a height of 4.1 metres! Access to the chamber was by a 5.8m long entrance passage, between 0.5m and 0.8m wide, in the cairn’s eastern side.
The passage is slightly curved and increases in height from 0.5m at the entrance to 1.2m at the inner end. One of the passage lintels partly collapsed while the chamber was still in use and stonework constructed at the north side to support it.
Unlike other chambered cairns in Rousay, the passage had not been blocked after Lairo went out of use.
Both passage and chamber are aligned east to west, slightly askew to the axis of cairn body. To Davidson and Henshall, the chamber “is impressive for its size and height, and the original design would have been even more so.”
The original chamber was roughly rectangular with orthostatic dividers creating three compartments. But according to the excavators, the builders’ plan to raise “the loftiest vault of its type in the north of Scotland” was not completed. 
Before the chamber had been built to roof height, an additional skin of walling was added to both sides of the first two compartments and across the entrance to the end cell, blocking it off. This masonry was built against the original walls and not tied in. Stone struts were built into the upper parts of the lining walls to prevent them shifting inwards. 
Arranged irregularly in the walls were four recesses, three of which contained human remains – a skull and other bones in the lower part of the south-western recess; a “burial deposit” in the lower north-western recess and a human skull and bones in the upper north-western recess.
Davidson and Henshall’s “tentative explanation” for the alterations was that they were an attempt to convert the stalled chamber to a Maeshowe-type.
The end result was a long, narrow, slightly curved chamber measuring c3.3m long by a mere 0.6m wide.
Outside, the excavators found evidence of a “horn” on the northern end of cairn – “all but obliterated” by agricultural work. On the south side there were horns noted at both ends, making Lairo “the second long horned cairn to be recognised in Orkney, the first having been identified by J. M. Corrie at the Head of Work.” 
The hornwork at the eastern end, framed an entrance forecourt that would have been c27m in width.
Knowe of Lairo, Rousay