Hadrian's Wall is one of the most ambitious things the Romans ever built, which is saying something. Ordered by the emperor Hadrian during his visit to Britain in 122 CE, it stretched eighty miles from coast to coast across the north of England, a solid stone curtain twenty feet high, punctuated with forts, watchtowers and fortified gateways spaced a Roman mile apart. The whole thing took six years to build.

It wasn't purely military. The gateways served as customs checkpoints, funnelling traders and travellers through Roman-controlled passages, possibly extracting tariffs along the way. A Persian mystery cult dedicated to the god Mithras set up a temple beside it. A sacred spring nearby held 13,000 votive coins when archaeologists finally dug it out.

VoiceMap's self-guided audio tours, led by archaeologist Gary Devore, walk the Wall from the fort at Brocolitia to Housesteads, explaining how a road-builder's demolition job in the 18th century consumed much of what Hadrian left behind, and tracing what survives.