NHER 31431 (Monument record) - Possible medieval salterns and possible post-medieval fort

17 July 1989. NAU aerial photography.
Polygonal ?cropmark.
D. Edwards (NAU).

The cropmarks consist of two polygons; one surrounds an 'island' of 5m contour on Ordnance Survey, the other to the south coincides with a polygonal projection of the parish boundary. They are joined by a double ditched corridor. The immediate impression is that of a Civil War fort such as site NHER 13784 to the east is supposed to be. But would a parish boundary be altered that late? Is this simply a fortuitous combination of a meandering roddon and an island? But what then is the link joining them? Fascinating!
A CUCAP air photograph from 1968 (S2) shows the cropmark more complete and there are marks within the northern polygon that might be a gun platform.
E. Rose (NLA) 4 August 1995.

October 2002. Norfolk NMP.
The site comprises three saltern mounds (S1) centred on TF 6315 2243, TF 6316 2231 and TF 6319 2223, with a series of enclosing and radiating ditches (S2). The northernmost mound is sub-rounded to elongated in plan with a north to south length of 90m and a width of 55m. The central mound appears to be sub-rounded in plan, with a maximum diameter of 80m. The mound is represented by a 5m contour on the Ordnance Survey 1:10,000 scale maps (S3). The mound is surrounded by a sub-rounded to sub-angular ditch with five potential sides. There also appears to be a stretch of secondary outer ditch running around the northern end of the mound. There are five ditches radiating from the enclosing ditch running towards the northwest, northeast and southwest. On the northern side of the mound are three chevron-shaped ditch or pit like features, visible as low earthworks in 1946 (S1) and as negative cropmarks in 1968 (S2). The features are situated around the northern edge of the mound and are 18m to 23m in length. The southernmost mound is sub-rounded in plan with a maximum diameter of 55m. There are two parallel ditches running between the central mound and the southern mound, flanking a raised area that may be a potential causeway joining the two mounds.
The radiating ditches are probably simply drains or canalised saltmarsh channels, although it does appear that the central mound within the group has been deliberately enclosed, possibly to act as a defensive strongpoint. It has been suggested that the site may represent a seventeenth century Civil War fort, although there is also a reference to a fort in this approximate location in 1588 (S4). The raised nature of the saltern may have lent itself to a defensive or observatory vantage point overlooking the Great Ouse and indeed it may have been used during more than one conflict.
It is interesting to note that the parish boundary skirts neatly around the northern side of this mound, enclosing the large mound within King’s Lynn parish. This may be a deliberate act of enclosing a strategically significant fortification within King’s Lynn parish, but equally it may simply follow the meander of a relict saltmarsh channel.
M. Brennand (NMP), 25 October 2002.

April 2020. National Mapping Programme (NMP) Data Clean-Up.
An additional possible medieval saltern mound has been added to the group described above, located to the east of the larger central mound (centred at TF 6325 2232). Like the features described above, it was mapped from aerial photographs in 2002 as part of the Norfolk Coastal Zone NMP, but was omitted from the recording.
S. Tremlett (Norfolk County Council, Historic Environment Service), 21 April 2020.