So the purpose of these forts became not to prevent people going to and fro so much as to control and observe them. The forts in particular, became a place where a kind of customs scam was imposed on those trying to do business on one side or the other. So maybe it's better to think of the wall not so much as a fence but rather as a spine around which control of northern Britain toughened, hardened and prospered. If we can now imagine Hadrian's Wall as not such a bad posting, it's because our sense of what life was like at the time has been transformed by one of the most astonishing finds of recent archaeology - the so-called Vindolanda Tablets. They're scraps of Roman correspondence, jottings, scribblings and drafts of letters thrown away as rubbish by their authors almost 2,000 years ago. For 25 years, archaeologists here have been digging up these letters, 1,300 of them, from seven metres below the ground. Up they've come, lovingly separated from dirt, debris and each other and painstakingly deciphered. At once poignantly fragile and miraculously enduring, the voices of the Roman frontier in the windy North Country, loud, clear and strong.