In pictures: Tarragona's death-defying human tower competition returns

Emotions were high as the heart-pounding tradition of building human towers made a return to Tarragona, Spain, where thousands of spellbound spectators gathered for the city's biennial competition.

Over 40 'colles' (teams) gathered in the historic Tarraco Arena Plaça, a former bullfighting ring, to take part in the event, now in its 29th edition since first debuting in 1932.

Jaw-dropping photos capture the sea of people watching on as hundreds of brave participants rose higher and higher in their 'castells'.

Here are some of the most stunning images from the event: