In Catalan the word 'castell' means castle.

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. (1)

Casteller from Mike Randolph on Vimeo.

'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.' (2)