The tradition of building human towers, or Castells, dates back to the 18th century and takes place during festivals in Catalonia, where colles, or teams, compete to build the tallest and most complicated towers. The structure of the castells varies depending on their complexity. A castell is considered completely successful when it is loaded and unloaded without falling apart. The highest castell in history was a 10 floor structure with 3 people in each floor. In 2010 castells were declared by UNESCO one of the Masterpieces of the Oral and Intangible Heritage of Humanity. See more news-related photo galleries and follow us on Yahoo News Photo Tumblr.