My brother David travels the world for work and pleasure. Here are his photos from his visit to the Concurs de Castells (City of Human Towers) festival in Tarragona, Spain.

This competition is held every two years in October, with the aim of creating the tallest tower amongst 32 teams.

The floor of the arena is packed tight with participants, forcing them to literally walk over each other

The strongest participants form the pinya, or base of the tower

The lightest participants form the upper levels. A child, the enxaneta, topping the structure

A strong base is essential

Once all the castellers of a team are locked into place by their arms, music begins to signal the start of the tower building

The sweet taste of victory

Dismantling a tower, or the collapse of one, can be dangerous and result in injuries

Castellers are judged on their best three attempts out of five. The taller the tower the better.

The enxaneta making his/her way to the top