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THREAD. Once upon a time .... see those long pale strips w/ dark outlines leading from the fore- into the middle-ground of the photo? Hold onto your hats: #RomanoBritish #peat diggings close to then coast line & now in the Cambs #fens, dug before the mid-3rdC AD. 
2. A major flood from the sea in the mid-3rdC filled these #RomanoBritish peat diggings w/ the light-coloured silt you can see in the photo. Now the peat wetlands they were part of have disappeared except for their dark outlines. They’re top L of the central blue block on the map
The map is from eaareports.org.uk/publication/re…, one of the iconic Fenland Survey volumes all available for free download.
So why was so much peat needed? It’s generally accepted that, as the diggings lay so close to the Roman coastline (everything *inland* of the speckled area on this map), the peat was used to heat large containers of brine in order to make salt. (Map eaareports.org.uk/publication/re…)
4. Field-walking found clusters of the broken remains of the large, thick-walled pottery vessels (briquetage)used by #RomanoBritish salterers for evaporating brine so close together that, on a windless day, the haze from their peat fires must have been visible for miles
5. So, how did they do it? Channels were cut (or adapted) (Stage 1) for trapping salt water at high tide (Stage 2). The interlude of the next low tide gave time for sediments to settle out of the brine (Stage 3). The cleared brine was ladled into evaporation tanks (Stage 4), & ..
5a. ... when evaporation had reduced the brine to a thick enough consistency, it was then heated over peat fires (Stage 5) to drive off the remaining water. (For detail see p.137+ eaareports.org.uk/publication/re…). See how landscape history enables us to #walkinancientfootsteps? 😝 END
6. PS The silt filling those diggings now stands proud of the surrounding #landscape, recording the level of the peat into which they were dug & has since disappeared. At 1st glance they look like the ridge and furrow of medieval ploughing ... but they’re not 😝
