It is widely accepted that the Four poster tradition grew out of the Recumbent-stone circle tradition of Aberdeenshire at the very start of the Bronze Age. The earliest ancestors of the four poster are found in the hills north of Inverurie, where gross extremities in the scale of recumbent-stone circles have been found ranging from very large (50 metres diameter) to very small (5 metres diameter). In some of the smallest, the setting consists of six or eight stones, one within 45 degrees of south being only slightly bulkier or special compared with the others. In most of these, a clear rectangle appears stones if only the four largest stones are considered.
The builders of the four posters -- with their traditions in tow -- travelled south-west, heading for the metal-rich southern regions of Ireland. Around Perthshire, about 200 kilometres away from Aberdeen, an extremely dense cluster of four posters occurs. Many believe that it was here, in the fertile valleys of Strathtay and Strathmore, that the four posters became refined into neat squares, averaging 12 square metres in internal area, placed on neat levelled mounds with Cists or cremations near the north east stone. Situations were chosen both for their proximity to communities (although this is less the case than with earlier monuments) and for the views they commanded. The south west remains the focal point, with alignments on nearby notches in hills close to the major southern moonset frequently occurring. It should be noted that four posters are hardly exact astronomical observatories, they should be thought of more as a memento of home for Bronze Age travellers who were ill-equipped to undertake workings on the size of the grand Recumbent-stone circles of the soon distant north east.
Quite why there are so many four posters in Perthshire isn't quite clear. It is possible the tradition was carried on by the local community after the travellers had left, or that longterm trade led to the blurring of cultures. Either way, there isn't a single four poster in the next 300 kilometres to Ireland, suggesting the journeymen picked up pace and hurried down to the cultural crossroads of Machrie Moor on Arran, in the vicinity of which several four posters have been found and excavated. Once on Ireland but outside the south west there are two confirmed four posters, both on the east coast, suggesting a route down that side of the island, to the region around County Cork, where another proliferation occurs. The radiocarbon dates for remains from this group are later than those for the others in Scotland which confirms the progression in construction.
It seems a reversion to some old habits takes place here, the southern or south west stone becoming higher and thicker, like a miniature recumbent from the Recumbent-stone circles. Another stone was added, whilst the two stones furthest away from the 'recumbent' became higher and thinner like the 'portal' stones of the Aberdeenshire circles yet on the wrong side! Eventually, the design was consolidated into what is known as the Munster stone cirle tradition.Evolution