The Human Towers (known in Catalan as "castells") have been one of the most important cultural traditions in Catalonia for more than 200 years. Once every two years the city of Tarragona hosts the most important human towers competition: the "Concurs de Castells." During the event, each team builds and dismantles its own human towers, which are between six and ten levels high. For their success, a crowded and stunning base of hundreds of people needs to be previously perfectly set up.