Ancient Welsh history has been turned on its head by the discovery of a huge Roman fort.

Archaeologists using special equipment to scan underneath the countryside have confirmed that a 2,000-year-old settlement at Dinefwr in Carmarthenshire would have been a huge centre of Roman military might.

Spanning an area greater than two rugby pitches, it indicates controlling our ancestors was far harder work than had previously been believed.

Emma Plunkett Dillon, the National Trust in Wales's archaeologist, said, 'At Dinefwr we appear to have one of the most significant Roman archaeological landscapes in Wales preserved under the turf and invisible on the surface.

'The forts are shown to be associated with roads, a civilian settlement and a possible bathhouse and the quality is remarkable.

'The site has the potential to enhance and possibly rewrite our understanding of the Roman conquest of Wales.'

Remains were initially discovered in 2003, but only now has it been brought to light just how large the settlement is.

Two overlapping Roman forts at the site almost certainly date to the 1st century AD.

The later fort was surrounded by an impressive set of defences. The earlier fort was even bigger and could be the largest garrison fort ever found in Wales.

The forthcoming dig is part of a project to restore the landscape of Dinefwr Park and Castle.

Gwilym Hughes, of Cambria Archaeology, said, 'The discovery could transform our understanding of the Roman conquest of South-West Wales and our intention is to determine the character of the buried archaeology through this work.

'Although we can tell a lot from the geophysical survey, excavation will provide the critical dating evidence from items such as coins and pottery that may confirm when the forts were built and abandoned.'

The organisation's Dr Nikki Cook added, 'We knew about the Roman settlements in the area, but this means the idea that most of the Welsh were happy about Roman occupation does not ring true.

'They wouldn't have had such a huge military facility, with the ability to contain so many legionaries, if they didn't need them.

'Most of the population were eventually Romanised, because there were a lot of benefits to it, but it may not be until a lot later than we had thought.'

Tony Robinson and the Time Team will be filming live from the excavation on July 2 and 3 as part of their 'Big Roman Dig' week.