After Offa’s Dyke last week, Tony Robinson moves on to the Peak District, where the Derbyshire Portway awaits.

The craggy Portway runs from the north of the county down to the edge of Nottingham and is presumed to be prehistoric.

But what, so far from the sea and so high up, is a shark’s tooth doing buried here?

Just one of the riddles that Tony is hoping to solve.