It consists of fortifications built by soldiers in about 70 AD as they moved into a war-torn Celtic kingdom to rescue its pro-Roman ruler, and was discovered at Roecliffe, North Yorkshire.
Archaeologists - from the Co Durham-based consultancy Northern Archaeological Associates - have located not only an eight-acre Roman fort, but also the earthwork defences erected to protect the site while the fort was being built.
It is the first time that such earthworks have been excavated in Britain. About 500 yards have been detected so far.
The soldiers who used the fort were on the side of Cartimandua, queen of Brigantia, Britain's largest native kingdom, who had been overthrown by her outraged former husband, Venutius, whom she had just divorced in favour of her lover, previously Venutius's armour-bearer.
Venutius led many of the tribes of Brigantia in revolt against his ex-wife, who had openly collaborated with the Romans and who probably had an official treaty of friendship with them.
She was toppled and had to be rescued by her Roman allies.
The fort was built next to a prehistoric trackway and appears to have had the job of guarding a bridge over the river Ure. Excavations - directed by Mike Bishop, a leading authority on Roman military equipment - have turned up fragments of weapons, armour and cavalry equipment. They suggest the fort was occupied by a mixed force of Roman legionaries, Roman cavalry and mounted native British troops who were loyal to Cartimandua.
This tripartite mixture at a Roman military installation is extremely rare.
The Roecliffe fort's defensive earth walls - probably about 15ft high - were faced front and rear with horizontal wooden planks held in place with vertical posts and possibly whitewashed, Mediterranean-style, and decorated with criss-crossed red lines to suggest stonework.
There would also have been up to 20 wooden towers along the walls, while inside the fort itself the single-storey wooden barracks appear to have been roofed with red tiles.
By around 85 AD, Brigantia had been fully integrated into the empire. Roecliffe fort was abandoned in the mid-80s and appears to have been replaced by a new fort a mile away at Aldborough, a site which three decades later became the Roman administrative centre for all Brigantia.
It is not known from the historical sources what happened to Venutius, Cartimandua or her lover.Reuse content