The Castles, near Hamsterley, County Durham, is an archaeological conundrum.
A massive rectangular dry-stone enclosure, some 75 metres by 90 metres, it has been described variously as an Iron-Age fort, a Roman penal colony, a native sub-Roman or Anglo-Saxon encampment, and a Romano-British farmstead.
Time Team's main objective at the mysterious site is to try to discover its true function and date.
