The Roman town at Caistor St Edmund was up to three times larger than was previously thought, a new dig has revealed.
It has long been known that the streets of the Roman town of Venta Icenorum extended beyond the defensive wall which can be seen at the site.
But, in August this year, Caistor Roman Project, a community archaeology team formed in 2009, excavated a large trench on land about 300 metres from the town walls, with the aid of an £84,000 Heritage Lottery Fund grant.
Parts of the enclosure ditch have been recognised on aerial photographs since the 1960s, but the section identified by the air photo interpretation team, part of Norfolk County Council's historic environment service, was a long way north of the town.
The latest excavation has demonstrated clearly that the new section of the ditches is definitely of Roman date and that the Roman town was surrounded by concentric ditches, a mile and a half long, enclosing an area of nearly 89 acres – which is more than two and a half times the area of the walled Roman town.
That information, together with evidence from a 2015 series of test pit digs in local gardens, adds weight to the evidence that Roman archaeology extends beneath much of the current village.
Dr Will Bowden, of the University of Nottingham, who has been directing research at Caistor Roman town for 10 years, said 'This discovery dramatically changes the story of the Roman town and shows that community archaeology can contribute to discoveries of national importance.'
The purpose of the ditches is not clear. Archaeologists say the perimeter is too large to have been used practically for defence and they question whether it was a 'grand urban vision' which was never realised.
Venta Icenorum was the capital of an area encompassing modern Norfolk and parts of Suffolk and Cambridgeshire.
Recent major excavations by the University of Nottingham traced the life of the town from its origins in the 1st century AD to its eventual disappearance as an urban centre.
Caistor is said to be unique among the greenfield capitals of Roman Britain in the extent of its Anglo-Saxon occupation, which indicates that it remained a centre of political importance long after the Roman period.
On Saturday, January 14, there will be a one-day conference at the University of East Anglia bringing together all the results so far from the site.
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