Chepstow, town, Monmouthshire, southern Wales. Well situated as a transport centre, Chepstow is located on the Severn Estuary at the mouth of the River Wye, adjacent to the Severn road bridge and the M4 motorway. Chepstow's port, once important, is today only accessible to smaller boats. The town's economy is based around tourism, the agricultural trade, and light industry. The site has been settled since prehistoric times, reflecting its strategic position controlling the entrances to the Severn and Wye Valleys. Chepstow became an important fortress town on the Welsh-English border in the 12th century, when the Normans built the castle (1120-1130) which is still the dominant landmark of the town. King Edward I extended it and it remained impregnable until the 17th century, when Oliver Cromwell's guns breached its walls during the Civil War. In the 13th century the 2-m (6-ft) thick Portwall was built to protect the side of the town not protected by the river. Much of the wall is preserved, and the town gate leads to steep and twisting medieval streets. Chepstow is often used by tourists as a base for exploring the scenic Wye Valley, within which Tintern Abbey is situated. There is a racecourse just outside the town. Population (1981) 9,233.