Chepstow is technically the easternmost town in Wales, pinned against the Gloucestershire border on the tidal Wye, about two miles above the river's confluence with the Severn. The Severn Bridge - the older of the two great crossings - touches down on its outskirts, and the town has spent most of its history as a gateway. The Normans came through here. So did the timber and bark of the Wye Valley and the Forest of Dean, loaded onto ships and sent down the Severn estuary. In the late eighteenth century tourists discovered the Wye Valley, and Chepstow became the launching point of the picturesque "Wye Tour" - one of the first organised tourist itineraries in Britain. The town today has about twelve thousand residents and a steady commuter trade to Bristol, Newport and Cardiff.

FitzOsbern's original keep is the heart of Chepstow Castle, and it is the oldest piece of secular stone architecture surviving in Britain. Successive owners added curtain walls, gatehouses, towers and a marvellous set of timber doors - the Chepstow Castle doors, still on display inside, are among the oldest castle doors in Europe. The Marcher lords ruled Striguil, as the lordship was then called, from these walls. Charles I's forces held the castle in the English Civil War, and Parliamentary cannon eventually broke it open; after the war it served as a state prison, then slowly slipped into the ruined splendour you see today. From the river below, the castle still looks impregnable - which is exactly the impression Norman masons spent generations building.

Down in the walled town, the Benedictine Priory of St Mary was founded in 1067 alongside the castle. Its Norman west doorway survives, weathered but intact, and inside are Jacobean tombs and centuries of accumulated alterations. The Old Wye Bridge below the castle dates from 1816 - a cast-iron span replacing a succession of wooden predecessors, and an early monument to the Industrial Revolution's appetite for graceful engineering. The streets between bridge and priory still follow the medieval pattern: narrow, sloping, lined with houses that lean into the hill. Some of those houses, like Gwy House from 1796, are genuinely fine. The Town Gate, a 13th-century arch still spanning High Street, makes the boundary between old and new exactly where it always was.

Chepstow was a shipbuilding town. One of the First World War's National Shipyards was thrown up here on the riverbank, and the heavy engineering tradition continued for decades - the Mabey Bridge works prefabricated bridges and, later, wind turbine towers, sending vast steel sections out by road and barge. The racecourse opened in 1926 in the grounds of the now-ruined Piercefield House, a mile north of the centre, and has hosted the Welsh National every year since 1949. Piercefield's wooded grounds, threaded by the Wye Valley Walk, were once the showpiece of the Wye Tour. Even today the views over the river from the cliff path are the kind that made eighteenth-century travellers stand still.

Wales begins or ends here, depending on which way you are travelling. Cross the old bridge eastbound and you are in England within fifty yards. Cross westbound and you are pointed up the Wye Valley toward Tintern Abbey, Monmouth and the deep folds of Welsh upland. That hinge quality is what Chepstow has always done well - it has been a Norman frontier, a port, a tourist gateway, an industrial node, a railway junction. The castle on its cliff is still the first thing you notice, and that is appropriate. Nine hundred and sixty years on, it is still doing its job.