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Promontory fort, situated on a natural defensive strongpoint, an Iron Age fort which was succeeded by a Pictish fort. The original access would have been along the narrow flat-topped ridge which runs north from Rock House. the promontory neck now cut by the access to Green Castle Fisheries.. The hollow between the southwest extremity of Green Castle and the Port Hill has been raised and levelled to accommodate the fish processing, and the area southeast of the fort has also been built up. The Statistical Account (1794) records 'ruins…of some old buildings' on the top of Green Castle. In 1967 the OS recorded a slight earthen bank on the south and southeast sides of the flat top of Green Castle, noting that cliff erosion had exposed a cross section of bank in which a large quantity of charcoal, but no vitrified material, could be recognised: no trace of buildings was observed. Field visit 1976 observed that slumping along the fortified edge appeared to be worsening. Charred beams could clearly be seen in the section and a few sherds were collected from the eroding. At that time the surviving habitable width of the site was circa 15 m on average, the length of the upper platform at the southwest end of the site measuring circa 70 m. Seven seasons of excavation were carried out by I Ralston between 1976 and 1982. A resistivity survey in 1976 did not provide useful results, only suggesting that the interior of the site was relatively stony. Removal of the turf over the interior revealed that most of area was covered by low stone platforms, a single stone thick, built of either beach pebbles or more angular fragments and frequently edged by more substantial stones. These covered the entire summit of the promontory, running down the seaward slope to the apex of the site and masking the surviving remnants of the rampart. These appear to be fish drying platforms which post-date the 1794 Statistical Account, and probably of 19th century date although they had in part destroyed earlier features they had also helped stabilise parts of the site, in particular remains of the defences. The promontory was also used for drying nets and blankets in the earlier 20th century, their poles cutting through platforms. Below the platforms the excavation recorded several periods of activity on the site. The earliest phase of defence was a single palisade located below the crest of the promontory, marked by the slight traces of a slot which runs slightly obliquely to the main wall. The palisade trench produced an Iron age rim sherd, whilst a number of pits were recorded in the interior. The main occupation horizon produced clear evidence of metal-working including mould fragments and parts of bowl furnaces. Find included pottery, a perforated whetstone of schist, pot lids and hammerstones, mould fragments, fragments jet bracelets, and a small amount of animal bone. The upper surfaces of pits were scored by ard-marks, parallel to the axis of the site, indicating a period of cultivation before further defensive works were constructed in the Pictish period. An ard-mark cut into the top of one of the pits produced a complete small glass ring. The first phase of Pictish activity comprised a palisade line backfilled with substantial beach cobbles. This was subsequently replaced by a timber-laced rampart, comprising a single line around the landward part of the site. This defensive wall contains both longitudinal and transversal timbers that have been burnt, much of the sand in the core of the rampart is fire reddened. However, temperatures in this destructive conflagration seem to have been insufficient to cause vitrification. The timbers are of oak, the horizontal elements with clear evidence of mortices into which the vertical elements were set. The core of rampart contains considerable quantities of sand, small cobbles and more sizeable blocks. It was not clear from excavation whether there was an internal revetment. Samples of oak charcoal from timbers produced radiocarbon dates of 665-944 AD. A number of structures, including stone-built, have been identified in the interior, including one rectangular built stone structure with rounded corners measuring circa 8 m by 4 m. Following the final season of excavation Ralston suggested that entire defensive and early occupational evidence from the site may fall within the Pictish period. The approach causeway shows no evidence of artificial construction.
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