 The first evidence of the exploitation of iron and coal in the valley is found in the Roman period, with iron working known from sites at Monmouth, Trellech and elsewhere, as well as in the adjoining Forest of Dean.The medieval boroughs of Goodrich and Chepstow, at each end of the Wye Gorge, may have originally been established at this time.Closely following the River Wye, Offa's Dyke was built in the 8th century under King Offa to mark out the boundary between England and Wales and is, today, the longest archaeological monument in Britain.