The tradition of building the tallest human towers has returned to the Spanish city of Tarragona in a spectacular biennial competition, drawing thousands of awed spectators.
Remarkable pictures show crowds packed into the city to watch the Catalan tradition as competitors defied gravity and formed the towers.
The 'castells' are human towers formed by competitors standing on the shoulders of one another.
Teams of up to 500 men, women and children compete to build the tallest tower - which can be as many as ten levels tall.
The highest and most complicated tower is dubbed the winner, with some reaching over 40ft tall in recent years.
Members of 'Colla Jove Xiquets de Tarragona' team form their castell during the final of the castells contest in Tarragona
Children of Xiquets de Reus build the final part of the human tower during the Concurs de Castells competition
The tradition of building human towers or 'castells' has returned to the Spanish city of Tarragona in a spectacular biennial competition
Members of the 'Castellers de Vilafranca' team are pictured in a stunning topshot
Children of Xiquets de Reus build the final part of the human tower during the Concurs de Castells competition
Colla Castellera Jove de Barcelona participates in the Concurs de Castells competition, seen bracing at the very top
Thousands gathered to watch the spectacular feats of complex human towers today
Members of Castellers de la Vila de Gracia precariously perching at the very top of their tower
Members of Colla Jove Xiquets de Tarragona grimace as they build a human tower
Valeria, 11, reacts after climbing to the top of a 'castell' or human tower during the 29th Human Tower Competition
A mother holds her daughter in her arms after completing a human tower by Colla Jove Xiquets de Tarragona
Some teams like 'Colla Joves Xiquets de Valls' fell as they attempted to form one of the human towers at the event
'Colla Jove Xiquets de Tarragona' build a human tower during the 29th 'Castells' human tower competition
Members of Colla Jove Xiquets de Tarragona celebrate the victory after building a human tower
Many different teams compete to create the tallest and most complex human towers
'Colla de Castellers de Barcelona' team form their castell, or human tower, during the final
The Catalan tradition dating from the 18th century was inscribed on UNESCO's Intangible Heritage of Humanity in 2010 and was described as an 'integral part of Catalan cultural identity'.
Competitors 'Castellers de Vilafranca' were crowned as winners after constructing two ten tier towers with three and four people in each.
More than 20,000 people come to watch the participants, with points awarded to teams depending on the difficultly and height of each castell.
Group members of 'Xiquets de Reus' form a human tower, surrounded by thousands of observers
Tense attendees watch on in anticipation as Tarragona hosts the 29th Castells Competition
'Colla Vella dels Xiquets De Valls' team during the final of the castells contest in Tarragona, Catalonia region, Spain
The Castellers of Vilafranca celebrate after wining the 29th Castells competition for the second consecutive time
The Castellers of Vilafranca won the 29th Castells competition of Tarragona with their incredible towers
'Colla Jove Xiquets de Tarragona' build a human tower, with a child climbing over the shoulders to get to the top
Many of the teams use small children to get to the very top and make their human towers even taller
Members of 'Colla Vella dels Xiquets de Valls' fall down as they build a human tower
Members of 'Colla de Nens del Vendrell' during the final of the castells contest in Tarragona, Catalonia region, Spain
A little girl member of Xiquets de Reus cries with happiness after successfully dismantling a human tower
A stunning aerial photograph shows 'Colla Jove de Tarragona' as they form a 'Castell'
The teams have five rounds to build their best towers - and their final score comes from the total points gained for their best three attempts.
These are assessed by a panel of seven judges, who are said by competition organisers to be 'experts on the human towers'.
The tradition of building the human towers is believed to have originated from performances by 18th century dance groups in the area.
The event - popular with both locals and tourists - has been declared part of the Lists of Intangible Cultural Heritage established by Unesco.
Members of Xiquets de Reus celebrate the victory after building a human tower during the Concurs de Castells competition
The teams have five rounds to build their best towers - and their final score comes from the total points gained for their best three attempts
Nens del Vendrell build a human tower during the Concurs de Castells competition in Tarragona, Spain
The tradition of building the human towers is believed to have originated from performances by 18th century dance groups in the area. Pictured is a human tower made by colla Moixiganguers d'Igualada
'Marrecs de Salt' build a human tower during the 29th 'Castells' event, which draws huge crowds
The Nens del Vendrell build a human tower during the Concurs de Castells competition in Tarragona, Spain
Pictured is the swarm of thousands crowded in The Tarraco Arena to watch the event
The 'Colla Vella dels Xiquets De Valls' team pictured in their human tower at the competition today
'Colla de Mataro' and 'Colla de Vilafranca' teams take part in the final of the castells contest in Tarragona