Chepstow Castle is perched on a high cliff next to the River Wye, close to the Welsh and English border. It was built in the mid-11th century, following the Norman Conquest, and is Britain's oldest surviving stone fortification built after the Roman occupation. It was expanded over several centuries as military technology advanced. 

The first major major expansion came in the late 12th century, with the renowned knight, soldier and statesman, William Marshall, 1st Earl of Pembroke using his experience of French military architecture to bolster the castles defences, which are named after him.