Why Build a Castle?

S1, E1: Peter and Tom set to work straight away learning the skills of the medieval stonemasons to construct a beautiful spiral staircase. After digging stone out of the quarry they take it to the tracing floor, where every stone is marked out using the most closely guarded knowledge of the medieval castle builders: geometry. Then each step is hand carved, a three-day task, before being winched into place using the treadmill-powered crane.