Dan Cruickshank presents the series exploring famous buildings. The warrior dream of the medieval age was to build the world's first invincible fortress. Harlech Castle was that fortress, striking terror into the hearts of those who confronted it and taking military strategy into the modern age. Even today the castle is the most awe-inspiring in Britain - it commands a dramatic outpost on the Welsh coast and was the focus of the most bitter conflict between the English and Welsh as Edward Longshanks, King of England, pitted his wits against Llewellyn ap Gruffyd, Prince of Wales. Hiring the most renowned castle builder in the world - Master James of St George who worked in Italy and France - Edward Longshanks was determined to build an extraordinary fighting machine right in the heart of enemy territory. James invented a castle that quite literally grew out of the Welsh granite beneath it - taking as his model the largest crusader castle in Syria - and improving on it. Harlech re-invented the architecture of the castle. And around it was played out a fight to the death - the outcome of which would decide the shape of modern Britain.