Evidence of massive fortifications dating back at least 2,400 years has been unearthed at the site, five miles north-west of Windsor at Taplow in Buckinghamshire.
Excavations are revealing the remains of a 3m-deep, 9m-wide defensive ditch, backed by a substantial timber-faced rampart linking what appears to have been a series of 5m-high wooden towers.
Like the much later castle at Windsor, its role was to guard the strategically and commercially important Middle Thames Gap between the once heavily wooded Chiltern Hills and the once equally forested hills of Berkshire.
Throughout history, traders and armies have used the river as the only easy way of getting from the London Basin into the Oxford Plain.
In pre-historic times, the route was the main means by which much of Britain imported valuable continental bronze tools, ornaments and weapons. Whoever controlled the entrance to the Middle Thames Gap would have enjoyed exceptional wealth and power. The fortress may have beenhome to the rulers of a local tribal kingdom. The site was of royal importance in the Dark Ages and nearby Windsor has been a royal centre since Medieval times.
The newly discovered pre-historic fortress was at its most imposing in the Early Iron Age - sometime between 700BC and 400BC. But the earliest fortifications on the site may have been built as long ago as 1000BC - the Late Bronze Age.
A team of experts from Oxford Archaeological Unit arepiecing together the fortress's history. Gruesome evidence, gleaned during the excavations so far, suggest that a member of an enemy tribe or clan was captured and sacrificed in order to ensure the fortress's invincibility.
A skeleton - probably a sacrificial victim - was found buried in front of the monumental main gateway. Archaeologists believe he was ritually interred during the construction of the defences - probably as an offering to the gods, a religious gesture to guarantee divine protection for the fortress.
However, this pre-historic insurance policy does not seem to have worked. Archaeologists have discovered that the fortifications were burnt to the ground - presumably as a result of a massive enemy attack. The excavations are directed by archaeologist Tim Allen and have unearthed some of the burnt timbers which had once formed part of the defensive walls.
Further archaeological evidence suggests the six hectare site contained many houses and may have been home for up to 200 people.
The discovery, together with Neolithic, Bronze Age, Late Iron Age and Roman artefacts found on and around the site, reveals that Taplow is probably one of the oldest continuously inhabited places in Britain. It is already well known for its later remains, including a Dark Age, Anglo- Saxon royal burial mound.