Every year in Spain, a Catalan tradition of building Castells—human towers reaching up to 10 stories—takes place. Teams called colles compete to build the tallest and most complex tower made only of human beings standing atop one another. Teams are considered to have been successful if they can build and deconstruct their towers without a fall.

1. Members of the "Castellers de Villafranca" get into position to form their human tower during the 26th Human Tower Competition in Tarragona, Spain, on October 2, 2016.
Emilio Morenatti / AP
2. Members of the Castellers form a human tower during the Saint Merce celebrations in San Jaime square in Barcelona, Spain, on September 25, 2016.
Manu Fernandez / AP
3. Members of "Vella de Xiquets de Valls" form their human tower during the 26th Human Tower Competition in Tarragona, Spain, on October 2, 2016.
Emilio Morenatti / AP
4. Members of the colla 'Vella de Valls' build a human tower during the 26th Tarragona Competition on October 2, 2016.
David Ramos / Getty
5. Castellers de Sants start to form a human tower in Tarragona on October 2, 2016.
Albert Gea / Reuters
6. Colla Vella Xiquets de Valls form a human tower while a supporter applauds in Tarragona on October 2, 2016.
Albert Gea / Reuters
7. Members of the "Castellers de Villafranca" build their human tower on October 2, 2016.
Emilio Morenatti / AP
8. Members of "Vella de Xiquets de Valls" fall as they try to complete their human tower during the 26th Human Tower Competition on October 2, 2016.
Emilio Morenatti / AP
9. Colla Joves Xiquets de Valls fall down after forming their tower on October 2, 2016.
Albert Gea / Reuters
10. In this Saturday, October 1, 2016 photo, members of Xiquets de Hangzou celebrate after completing their human tower.
Emilio Morenatti / AP
11. Castellers de Vilafranca form a human tower on October 2, 2016.
Albert Gea / Reuters
12. Members of the colla 'Vella de Valls' build a human tower on October 2, 2016 in Tarragona, Spain.
David Ramos / Getty
13. Castellers de Sants start to form their castell on October 2, 2016.
Albert Gea / Reuters
14. Castellers de Vilafranca start to form their human tower on October 2, 2016.
Albert Gea / Reuters
15. Members of the colla 'Castellers de Vilafranca' fall down after they built a human tower during the 26th Tarragona Competition on October 2, 2016 in Tarragona, Spain.
David Ramos / Getty
16. In this Saturday, October 1, 2016 photo, Xiaotong Feng, 24, from China, reacts as she looks at members of Xiquets de Hangzou trying to complete their human tower.
Emilio Morenatti / AP
17. Castellers de Vilafranca fall after forming their human tower on October 2, 2016.
Albert Gea / Reuters
18. Colla Jove Xiquets de Tarragona start to form a human tower in Tarragona city on October 2, 2016.
Albert Gea / Reuters
19. Castellers de Sants form a human tower on October 2, 2016.
Albert Gea / Reuters
20. Members of the 'Xiquets de Hanghzou' take pictures during the 26th Tarragona Competition on October 1, 2016 in Tarragona, Spain.
David Ramos / Getty
21. Members of "Vella de Xiquets de Valls" try to complete their human tower on Sunday, October 2, 2016.
Emilio Morenatti / AP
22. Members of the "Castellers de Villafranca" react after completing their human tower during the 26th Human Tower Competition in Tarragona, Spain, on October 2, 2016.
Emilio Morenatti / AP