© PAThe fort is on the site of the Wallace Monument in Stirling
Experts are hoping to discover more about a tribe that lived in the fort below Abbey Craig in Stirling, on the site of the National Wallace monument.
The fort was destroyed in 780 AD, more than 500 years before William Wallace watched the English army approach.
The dig is one of a series of events to mark Scottish archaeology month.
Archaeologists first discovered the 1,300-year-old fort 10 years ago and concluded it was engulfed by a ferocious fire that fused together - or vitrified - the stone walls during a siege.
'Warlike past'
The stronghold is thought to have been called Iudeu.
Stirling Council archaeologist Murray Cook said the fort was occupied at a time when mainland Scotland was ruled by the ancient tribes of Picts, Celts, Britons, and Angles.
"Scotland has more known vitrified forts than anywhere else in Europe and here in Stirling we have our own that reflects our warlike past," he said.
"Despite a wealth of information known about the area there is relatively little known about this fort, however.
"The flames which lit up the sky would have been visible for miles around."
The dig will end on Monday.
That doesn't sound like normal man-made fire to me.