Fred takes a look at the 11th-century building programme undertaken by the Normans which resulted in mighty fortress cathedrals like Ely and Peterborough.At Peterborough Cathedral, Fred reveals the secret weapon the Norman builders had at their disposal - the stone arch - and demonstrates just how the early stonemasons constructed them. At Ely, Fred climbs high up inside the building to examine the alterations and additions made by later builders. Inspecting this construction masterpiece sees Fred scaling rooftop ladders to examine the incredible octagonal lantern built in the 14th century, an amazing feat of early engineering. Fred also has the lowdown on exactly how this feat was accomplished.Fred's final destination is Rochester, this time to examine a Norman castle rather than a cathedral. Here, he demonstrates how the tactics used all those centuries ago by attackers to try and destroy tall towers bear a startling resemblance to the way he used to pull down tall buildings.