This week, we head to Gloucestershire for a stroll along a section of Offa's Dyke — the great earthwork boundary dyke built along the Anglo-Welsh border by Offa, King of Mercia, and one of the most remarkable structures in Britain. We're joined by professor in archaeology Keith Ray, who reveals when and why Offa's Dyke was built, who the Mercians were, how they used the structure, and how the dyke is protected and maintained today.  To learn more about Offa's Dyke or plan a visit, go to www.english-heritage.org.uk/offas-dyke. Learn more about your ad choices. Visit megaphone.fm/adchoices