Team members climb over one another to add further layers to their tower during the 25th edition of the Contest Castells, which is held every two years.
The Guardian.com–The tradition of building human towers, or castells, dates back to the 18th century and takes place at festivals in Catalonia, where teams – ‘colles’ – compete to build the tallest and most complex towers.
A castell is considered successful when it is loaded and unloaded without falling apart. The highest castell on record was a 10 floor structure with three people in each floor.
See photo gallery on The Guardian.com: http://www.theguardian.com/world/gallery/2014/oct/06/human-towers-of-tarragona-in-pictures