>> the oldest people and the people, the tallest one and biggest one, in the base of the structure of the castell, but then you can find the children in the top. >> that's right. children. some as young as five years old climb atop the human towers and salute the crowd. >> translator: when i'm on top, i get nervous. >> a nine or rarely achieved ten level castell can exceed more than 40 feet in height. that's a long way up with very little protection. >> it's normally just for the children, the helmets, but also here in our group we have teeth protection for the children. it's important, the belt for protecting your back, but also for the people who climb up the castell it's important because it's a point of support.