A466 road about long and runs through the counties of Herefordshire and Gloucestershire in England, and Monmouthshire in Wales. It runs south from Kingsthorne, on the A49 south east of Hereford to Monmouth, crossing the A40. After crossing the River Wye at the Wye Bridge, Monmouth and Bigsweir Bridge near Llandogo, it follows a picturesque route south down the Wye valley through Tintern and Chepstow to the M48 motorway at junction 2. The road crosses the border between England and Wales at three places along its length: at Buckholt, Redbrook, and Bigsweir. It runs through an Area of Outstanding Natural Beauty, and
England–Wales border an exclave of Flintshire, between Bangor-on-Dee (in Wales) and Whitchurch (in England). Returning to the River Dee as far as Chirk, the boundary then loops to the west, following Offa's Dyke itself for about , and including within England the town of Oswestry, before reaching the River Vyrnwy at Llanymynech. It follows the Vyrnwy to its confluence with the River Severn, and then continues southwards, rising over Long Mountain east of Welshpool. East of Montgomery, the boundary again follows the line of Offa's Dyke for about , before looping eastwards to include within Wales a large area near Churchstoke. It