Azim Ahmed walks a section of Offa's Dyke, to explore what it has to tell us about our place in the world, and in the universe. This ancient archaeological wonder constructed by the Mercian King Offa has in some ways been the making of Welsh identity. But it also speaks of fascinating connections with Europe, and possibly the Islamic world. A visit to Knighton's Spaceguard centre, however, suggests that our planet, let alone Wales, may be but a mere speck in a vast and dangerous universe.