A team of more than 200 castellers from Spain build a "human tower" on Shanghai's Nanjing Road pedestrian precinct Sunday, May 23, 2010, as part of the start of Catalonian week at Expo 2010 Shanghai. A castell（等級） is a human tower built traditionally at festivals in Catalonia, a region of Spain. At these festivals, several colles castelleres, or teams, build and sustain a tower structure for a certain period of time.[Photo/Xinhua]