Castellers build castells (human towers)

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The tradition of building castells originated in Valls, near the city of Tarragona, in the southern part of Catalonia towards the end of the 18th century. Later it developed a following in other regions of Catalonia and, since 1981, when the first castell of 9 levels of the 20th century was built, it has become very popular in most of Catalonia.

A castell is considered a success when stages of its assembling and disassembling, can be done in complete succession. The assembly is complete once all castellers have climbed into their designated places, and the enxaneta climbs into place at the top and raises one hand with four fingers erect, in a gesture said to symbolize the stripes of the Catalan flag. The enxaneta then climbs down the other side of the castell, after which the remaining levels of castellers descend in highest-to-lowest order until all have reached safety.

The sash (faixa) is the most important part of their outfit, since it supports the lower back and is used by other castellers in the team as a foothold or handhold when climbing up the tower. This tasselled piece of cloth varies in length and width and depends on the casteller's position inside the tower and also on choice. The length of the sash ranges from 1.5 to 12 m, and usually is shorter for those higher up in the castell. Performing castellers usually go barefoot as to minimise injures upon each other as they climb to their position and also for sensitivity when balancing and to have better feel and hold each other.

The motto of Castellers is "Força, equilibri, valor i seny" (Strength, balance, courage and common sense).

Not a bad motto for life in general.  More info here.