Croeso i Gymru . The “Welcome to Wales ” sign flashed past as I crossed over the Severn Estuary, to find the landscape swathed in brooding clouds. Despite the characteristic weather, I was excited to begin my three-day road trip along the 160-mile-long border between England and Wales. Beginning in Chepstow – where an 11th-century Norman castle guards the southern gateway to Wales – the border carves a path north towards the Dee Estuary. I was loosely following the route of Offa’s Dyke, an 8th-century earthwork that divided the earliest Anglo-Saxon kingdoms from their Welsh counterparts. It is arguably Britain’s oldest border. My self-planned itinerary would take me along an ancient divide defended by crumbling medieval castles. I’d follow winding river banks into the Wye Valley , traverse the looming Black Mountains and hike historic sections of Offa’s Dyke Path on my way north. It’s a route I knew well, having spent the past three years travelling Britain’s borders while researching my new book .…