Promontory forts of Cornwall
Cornish promontory forts, commonly known in Cornwall as cliff castles, are coastal equivalents of the hill forts and Cornish "rounds" found on Cornish hilltops and slopes. Similar coastal forts are found on the north–west European seaboard, in Normandy, Brittany and around the coastlines of the British Isles, especially in Wales, Scotland and Ireland. Many are known in southwest England, particularly in Cornwall and its neighbouring county, Devon. Two have been identified immediately west of Cornwall, in the Isles of Scilly.
A promontory fort is a coastal headland, isolated from the mainland by a stone, turf or earthen rampart (univallate), or more than one (multivallate). Some promontory forts also have ditches. British promontory forts were constructed during the Iron Age, and remained in more-or-less continuous use into the early Roman period. Their function remains uncertain. They would have offered ready access to sea-routes but those built in particularly inhospitable settings may have had only occasional or seasonal use. Inland hillforts show signs of human habitation and other uses before and after the Roman era, but cliff castles were occupied sparsely, if at all. Some hill forts abandoned during or before the Roman era were reoccupied from the post-Roman to early medieval eras but in the same period cliff castles fell into disuse. Some were quarried for their building stone.
Treen is one of the few Cornish promontory forts to have been systematically excavated. Archaeologists believe it might have been developed from a Bronze Age site of ceremonial, religious or social significance to the surrounding community. Possible ancient contexts and uses of Cornish cliff castles have been a subject for study and speculation by antiquarians such as William Borlase. Modern sources agree that cliff castles may have served principally as prestigious sites for religious ceremonies, trade and administration, and that their defensive capacity may have been a secondary function.
The following cliff castles in Cornwall are listed by geographical location from the border with Devon at the Marsland Valley, west to Land's End and east via The Lizard to Cremyll overlooking Plymouth Sound. Unproven or uncertain sites are in italics.
The Dizzard (grid reference ) is an area of slumping cliff in the parish of St Gennys. The site is within the Boscastle to Widemouth SSSI and is known for its lichen communities which are of international importance. The promontory fort identified by the West Cornwall Field Club is probably a natural feature.
Castle Point (grid reference ) is a second possible site identified by the West Cornwall Field Club within the parish of St Gennys and the Boscastle to Widemouth SSSI. It is probably a natural feature.
Willapark (Boscastle) (grid reference ) is a headland to the west of Boscastle with a former coastguard lookout on the summit. The 110 m straight bank is indistinct to the south-west and up to 1.8 m high with a ditch on the landward side at its north-eastern end. The present path onto the headland may indicate the entrance. The fort overlooks Forrabury Common, a medieval field system.
Dinas Head (grid reference ) is on the western side of Trevose Head within the parish of St Merryn. The headland is a Scheduled Ancient Monument and included in a list of cliff castles awaiting classification. There is no sign of earthworks on the neck of the headland on photographs taken from aircraft.
(grid reference ) to the south of Treyarnon Bay, within the parish of St Merryn. The three headlands situated between White Cove and Wine Cove are registered as separate Ancient Monuments. The South West Coast Path passes on the east side of the entrance(s).   
Tregea Hill (grid reference ) (also known as Western Hill) is the site of a possible promontory fort on the headland overlooking the village and former port of Portreath. Tregea was recorded in 1205 as Trege possibly meaning ″homestead of the bank or hedge″ There is currently an earthen bank of approximately 0.75 m in height and 1.5 m wide at the base which cuts off the headland. At the eastern end coastal erosion has created a zawn (small inlet) and the bank appears to continue on the other side. Alternatively the bank could be a boundary or hedge.
Crane Castle (grid reference ) is situated on Carvannel Downs in the parish of Illogan, Castell Cliff was first recorded in 1530 and again in 1635. The antiquarian William Borlase visited the site in the mid–18th century and despite being situated on an eroding cliff the condition of the monument is similar today. Much of the cliff has eroded and a double rampart and ditch survives being 85 m (278.9 ft) and 71 m (232.9 ft) in length. The ramparts average 2.3 m (7.5 ft) in height and the ditch is up to 2 m (6.6 ft) deep and 1.5 m (4.9 ft) wide. Small scale excavations were made in 2012 revealing the depth of the ditches. The base of the inner ditch is 5.5 m (18.0 ft) below the (contemporary) top of the rampart, while the outside ditch was cut 1.5 m (4.9 ft) into the bedrock. Ditch fill of quartz indicates an attempt to impress from the landward side. The narrow area between the ditches and steepness of the bands suggest a ″killing zone″; an area where attackers, after over running the outer rampart, were °entrapped°. The only find was the rim of a finely made bottle from the Roman period, probably imported from Gaul.
Gurnard's Head (Cornish: Ynyal, meaning desolate one) (grid reference ) is a multivallate hillfort in the parish of Zennor and is one of only three to be excavated in Cornwall – the others being Maen Castle and Trevelgue Head. The inner rampart is the largest being over 5 m wide at the base and up to 2 m high although it was probably much higher as there is fallen masonry nearby. On the landward side there is an earthen bank with ditches on each side. Sixteen huts on the eastern side, sheltered from the prevailing wind show up as shallow scoops. Three were excavated (one partially) with few finds. Exact dating was not possible but the finds of an iron knife and iron buckle, spindle whorls, rubbing stone and pottery sherds indicate the middle second century BC for the initial occupation. The site is owned by the National Trust and is within the Aire Point to Carrick Du Site of Special Scientific Interest. 
Bosigran Castle (grid reference ) is an Ancient Monument within the parish of Zennor and owned by the National Trust. The cliff castle at Gurnard’s Head is within sight to the east. The headland is cut off by a, presumed Iron Age, 120 m stone wall which is up to 1.6 m high with a blocked central entrance. There is no external ditch and no evidence of hut circles or occupation.
Kenidjack Castle (grid reference ) is a multivallate hillfort in the parish of St Just. Two sets of triple ramparts with outer ditches have been built on the north east and south west sides. The northern ramparts are the best preserved and show the remains of stone revetting, with the inner one almost wholly built of stone. The outermost rampart of the southern set is lost by erosion and landslip. Shallow hollows and scoops within the headland may be hut circles or mining activity.
William Borlase, in the 1870s, recorded the traces of the bank and ditch of a cliff castle on Cape Cornwall (grid reference ), which had become indistinct by agricultural improvements. A survey in 1960 could not find any definite signs of a promontory fort but could see a possible ridge within the field, at the narrowest point on the neck adjoining the headland. Air photos do not show any evidence of a bank or ditch covering the ridge and it is concluded that a univallate castle did not exist here.
Maen Castle (Cornish: Maen, Men or Mayon, stone castle) (grid reference ) is an Ancient Monument owned by the National Trust, and situated between Sennen Cove and Land's End, within the parish of Sennen. The South West Coast Path passes the entrance. The ditch and external bank cuts off a small headland and it is thought to be one of the earliest cliff castles.
The West Cornwall Field Club excavated the site in 1939 and again in 1948–9. Three hundred pottery sherds from storage or eating vessels, found mainly from the one habitation site indicate a date between 800 and 400 BC. A 1986 National Trust survey found a ″kink″ in the line of the wall indicating an earlier field system was intregrated into the wall. It is conceivable that the field system could have been Early Iron Age or even Bronze Age.
Carn Les Boel
Carn Les Boel (grid reference ) is an Ancient Monument situated between Nanjizal and Gwennap Head in the parish of St Levan. The South West Coast Path passes nearby. There is some doubt as to whether the banks and ditch have been correctly interpreted as a cliff castle. One of the banks may date to the enclosure of Higher Bosistow Cliff in the 19th century, because apart from a gap of 5 m at Zawn Peggy, where the cliff has eroded, the bank and ditch follow the line of the cliff northwards for a further 300 m.
St Michael’s Mount
A complex of earthworks on St Michael's Mount (grid reference ) are considered to be the ramparts of a cliff castle. They were discovered in 1992 on the eastern side of the Mount and separate the granite outcrop from the harbour area.
Lankidden (grid reference ) is a univallate cliff castle between Coverack and Kennack Sands on the Lizard peninsula. The rampart is 100 m long and up to 4 m high and the ditch is 0.5 m deep. In the west part of the rampart and ditch have been lost to erosion.
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