Red hill (salt making)

Red Hill is an archaeological term in Britain for a small mound with a reddish colour found in the coastal and tidal river areas of East Anglia and Essex. Red Hills are formed as a result of generations of salt making, deriving their colour from the rubble of clay structures used in the salt-making process that have been scorched red by fires used to evaporate sea water to make salt cakes. They date from the Bronze Age, Iron Age and into the Roman period.

Small red mounds had been a noticeable feature of the coastal landscape in Essex and East Anglia for many centuries, but the first archaeological investigation into Red Hills and their function was not until 1879, when William Stopes excavated a group of them near Peldon, on the Essex mainland opposite Mersea Island. Originally Stopes thought that the mounds were Medieval in date, and were used for producing alkalis for glass making. However other investigations, such as that by John Christopher Atkinson, who compared them to similar mounds in Yorkshire, saw the mounds as prehistoric or Roman in date.

In 1906 the Essex Archaeological Society and Essex Field Club created the Red Hills Exploration Committee to identify the purpose, age and extent of the Red Hills, undertaking excavations at Langenhoe and Goldhanger, and later in 1909 at Canewdon on the River Crouch. Conclusions as to the exact nature of the type of activity carried out at the Red Hills were still lacking however, with archaeologist Flinders Petrie suggesting that the sites were where kelp and seaweed had been burned in order to create alkali solutions for soap and glass, whilst other archaeologists suggested pottery kilns. However some early comparisons to salt-processing sites in Brittany in the early Twentieth century lead to tentative suggestions that salt was at the heart of the Red Hills' purpose, with further excavations in Britain of sites similar to the Red Hills of Essex and East Anglia at Ingoldmells in Lincolnshire and Hook in Hampshire choosing this interpretation over the alkali explanation.

Ernest Linder's 1937–1941 excavations of Red Hills at Canvey Island in South Essex began to draw upon salt-making as the main suggestion for what had been occurring at these mounds. During the 1950s, 1960s, 1970s and 1980s further excavations were carried out around Southend-on-Sea and Canvey Island in South Essex, around the Dengie peninsula and Maldon in central Essex, and around Harwich and the Blackwater and Colne estuaries in North-East Essex. Red Hills and salt making at Salthouse (Norfolk) were also described by Hoskins. During these investigations much information was gathered both on the date and purpose of the Red Hills.

Over 300 Red Hills have been identified so far, mostly along the Essex and Norfolk coasts, with others in Suffolk and Kent. The vast majority of Red Hills are located on low-lying coastal flats in tidal estuaries and in back-waters like Hamford Water between Harwich and Walton-on-the-Naze in Essex. They take the form of low mounds, ranging in size from about 200 square metres (equivalent to a 16m diameter circle) to a hectare (equiv. to a 115m diameter circle). William Stopes identified one on Mersea Island near the Strood Channel which was 30 acres in size, but acknowledged that it may have consisted of more than one mound. The height of many mounds has been much truncated by ploughing, with others located close to rivers and the sea either being eroded away or covered with alluvial silt, but an average sized mound at Peldon in Essex, 0.2 acres in size, still stands at a height of roughly 1.3m (meaning a volume of about 1000 cu metres, equivalent to 1500 tons of earth).

The strata of the mounds is made up of tips of briquetage (broken fragments of fired clay from hearths, evaporation pans and other salt-making furniture which give the mound its red colouration), ash, charcoal and unfired clay. Most have large pits cut into the ground around them that have been lined with clay to produce a water-tight tank.

Several structures relating to salt production are found at Red Hills, whose purpose in the process is inferred from archaeological analysis and from analogies to Medieval and more recent techniques for obtaining sea salt.

Rows of oval clay-lined pits dug into the alluvium around the Red Hills are interpreted as tanks for holding sea water. These tanks are usually in groups, with those found at Red Hills at Goldhanger, Maldon, and at Leigh Beck at Canvey Island consisting of groups of three. Most tanks are between 1 and 2m in diameter, and around 1m deep, with a potential holding capacity of over 1000 litres.