An amazing set of photos released show thousands of people flocking together to create human towers. Formally, the competition is addressed as Concurs de Castells, which is a biennial event of Tarragona, Spain.

Human Tower
Castellers de Vilafranca start to form a human tower called castell during a biannual competition in Tarragona city, Spain.Reuters

In this sport, teams, each comprising 500 members or more, compete with each other at building the tallest human tower, which may or may not go up to as many as eight tiers. Participants on the heavier side build the foundation by staying on the ground, while the light-weighted ones climb the humans to make formations.

It is an integral part of the Catalan culture and over 20,000 people visit the arena to watch the spectacle. It is listed in UNESCO's cultural heritage list.

Human Tower
Castellers de Vilafranca celebrate after forming a human tower.Reuters
Human Tower
Castellers de Sants start to form a human tower.Reuters
Human Tower
Colla Joves Xiquets de Valls fall down after forming a human tower called castell during a biannual competition in Tarragona city, Spain.Reuters
Human Tower
Castellers de Vilafranca form a human tower.Reuters
Human Tower
A gathering of participants.Reuters
Human Tower
Colla Vella Xiquets de Valls form a human tower called castell, while a supporter applauds.Reuters
Human Tower
People display Esteladas (Catalan separatist flags).Reuters