The most significant linear earthworks in Swaledale and Arkengarthdale are the six dykes around Grinton, Fremington, and Reeth, which are marked in yellow on the Google Earth image above.
Two earthworks at the bottom of the image, appear partly to enclose a large bowl-shaped area of Harkerside Moor known as Harker Mires. The more-southerly and higher-level, L-shape earthwork, which is partly formed by a natural scar on High Harker Hill, is known as High Harker Dyke. The more-northerly and lower-level earthwork of the two is known as Harker Mires Dyke.
The other four earthworks are farther north, on either side of the River Swale, and now form parts of field boundaries. These four have been considered the surviving elements of two roughly parallel cross-dale defensive structures and are known collectively as the Grinton-Fremington Dykes. It has also been considered that all six dykes might have been part of a single defensive system, which might also have included a seventh dyke, on the south side of the river, opposite Marrick Priory. All have been considered to be prehistoric, but no-one yet knows with any certainty the antiquity or purpose of any of the dykes, or how they might be related to each other.
The four earthworks near Grinton on the south side of the River Swale are Historic England scheduled ancient monuments. The official listing reports can be seen here:
Linear earthwork at High Harker Hill, Grinton – 1012602 | Historic England.
Linear earthwork at Harker Mires, Grinton – 1012617 | Historic England.
Dyke 220yds (200m) W of Dyke House, Grinton – 1004043 | Historic England.
Dyke 270yds (250m) E of Dyke House, Grinton – 1004044 | Historic England.
There is a detailed plan, by Tim Laurie, of the Harker Mires Dyke and its relationships with several adjacent archaeological remains in his article here:
Early land division and settlement in Swaledale and on the eastern approaches to the Stainmore Pass over the north Pennines, in Upland Settlement in Britain: the Second Millenium BC and After, eds. Don Spratt and Colin Burgess, BAR British Series 143 (1985), see page 144 (11th page of the PDF).
These scheduled ancient monuments are protected from excavation, modification, or damage. However, when small cross-sections of two of the dykes became exposed, special permission was granted by Historic England and the Yorkshire Dales National Park Authority for SWAAG to conduct limited, supervised excavations at the exposed sites to discover what they might reveal. The reports on these excavations can be read here:
High Harker Hill Excavation, by Archaeological Services, Durham University on behalf of SWAAG, 2013.
Archaeological Recording of the Western Grinton Dyke, by SWAAG, 2016.
SWAAG member Will Swales investigated a 12th-century record that named the western Grinton-Fremington Dyke south of the river as Hodic. Findings from a study of the dyke’s relationship with other adjacent place-names and associated archaeological remains were published in the academic journal Landscapes (vol. 20.1, July 2019). A revised version, in two parts, can be read here:
Grinton-Fremington dykes | Swaledale and Arkengarthdale Place-names (wordpress.com).
Part of the article by Will Swales was to question whether the dykes might have been constructed as landholding boundaries rather than defensive barriers. A contrary opinion was expressed in a detailed article by two other SWAAG members, Alan and Judith Mills, and was published locally. It can be read here:
The Swaledale dykes revisted, by Alan and Judith Mills, in CBA (Council for British Archaeology) Yorkshire, Forum Plus, 2020, vol. 3.
In the SWAAG database, there are two entries related to the dykes around Grinton, Fremington, and Reeth in the Earthworks category PDF, scroll to the eighth entry, record no. 591, for Tim Laurie’s 2012 analysis of the High Harker Dyke, and scroll to the penultimate entry, record no. 998, for Stephen Eastmead’s LIDAR images of the dykes.
