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Dark Earth

18 August 2012

Looking around for some data as a note for some research I had a look through some old copies of Current Archaeology in my attic. I've got a small library up there and find them useful for looking up quotes and things, and research other people have ignored in a new paper, and so on. In issue 129 (June 1992) I found this on Dark Earth deposits which we are all familiar with in articles by Steve Mitchell in various SIS journals over the last few years. In 1992, it says, the Dark Earth was a hot topic among students of Roman Britain. Dark Earth, as such, covers the final Roman layers and lies between them and the Anglo Saxon levels – very often Late Saxon levels, 9th and 10th centuries. Various explanations have been aired. In Current Archaeology 124 the Dark Earth layer in Southwark was discussed, in its relationship to the Dark Earth deposit outside the boundaries of Saxon London. In 129 it is the dark earth deposit at Lincoln which is discussed, the presence of 4th century Roman coins has shown the city was in occupation right up to the withdrawal of Roman troops from Britain. Dark Earth deposits at Lincoln are attributed to dumps in the very late Roman period – when occupation at three key areas was abandoned. Where in Lincoln were these deposits located?

The Romans established a fort at Lincoln, on a high bluff with commanding views above the river Wytham. Later, Lincoln became a town and doubled in size, extending down the hill towards the river. The Dark Earth deposits occur at the foot of the slope – which may include hill wash. Hence, the facts appear to fit the Mitchell hypothesis, a rising water table, for whatever reason, led to the abandonment of riverside locations in the Late Roman period, from London to Lincoln, and St Albans and elsewhere. The Dark Earth is in effect the remains of what had become marsh and bog, probably used for animal pasture – even pigs rooting around. Now, this situation does not have to have existed for a long period of time, but it fits the evidence of what we know happened in the 4th century and immediately afterwards. There is that letter to Aetius for example, asking for Roman help because not only were they beset by Saxon invaders but by rising waters. In Scotland the Pictish movements also appear to have involved flooding. Most of the Picts simply moved inland – but even the lochs were expanding with rising amounts of water. They seem therefore to have adopted the tactics of the Saxons, invading foreign parts – which included Lowland Romanised Britain. We know there was a regression event in the Low Countries, the North Sea littoral as far as Denmark, and in the Fenlands on this side of the North Sea (including Lincolnshire and Humberside). What caused the eastern side of the country to flood is not clear. In Scotland, subsequent isostatic adjustment, the bounceback from the Ice Age, has led to uplift that has left early Christian sites of the 5th and 6th centuries high and dry – but in the south the adjustment has been downwarping as the north has moved up the south has gone downwards. Therefore, whatever happened on the coast in the Late Roman period is masked in the south, now under water. Early Christian churches have been swept away by the sea rather than stranded above high tide. Hence, something peculiar happened. It was big enough to bring a temporary halt to the isostatic bounce in Scotland and the north.

Saxon London had its Moorgate – the gate opening on to the moor or marsh, and its Fen Church, etc. These did not exist in Roman London which was located on the riverside. At Lincoln, like St Albans where the abbey was built halfway up a high hill above the river Ver floodplain where the Roman ruins can still be seen, the cathedral and castle are located in the Upper Town, on the hill. At a location halfway down the hill the archaeologists could find no evidence of the Dark Earth layer, whereas as the foot of the slope there was plenty of evidence of the Dark Earth. Now, we can all take part in a bit of visuals here and explore our own locales as the various burys around the country are assigned to the mid to late Saxon period. For instance, the bury at Aylesbury is the high ground on which the old town and the current market place stand – and its church. At Chesham the bury is high ground above the river Chess, nowadays a puny small stream of no repute but obviously once prone to flooding. The church, Pednor Manor house and farm, and the oldest parts of the town are all situated on the bury. At Hemel Hempstead we have precisely the same situation – the modern river Gade is a very small stream. It has crayfish, frogs and some small fish, but is otherwise overgrown with reeds and marsh plants. The bury is a couple of hundred yards away, and again the church, the manor and the older town are situated on this high ground, and the floodplain of the puny Gade is now a park with bowling greens, swings and things, but is perfectly flat. This is a very peculiar situation as the Chilterns are situated on porous chalk and rivers and streams are few and far between – yet in the early Saxon period there was a lot of water. Why?

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