Tens of thousands of revellers packed Pamplona and soaked each other in sangria Wednesday to kick off Spain's best-known fiesta: the San Fermin bull-running festival.
Swilling gallons of beer, wine and sangria, Spaniards and foreigners jammed into the main Plaza del Ayuntamiento to hear the traditional shout from a City Hall balcony: "Viva San Fermin".
Seconds later, a firecracker known as the "chupinazo" detonated, setting set off celebrations among a writhing mass of people dressed in white with red handkerchiefs, who sprayed each other with sangria.
The frenzy marked the start of a nine-day festival charged with alcohol, and laced with danger.
The most courageous, or inebriated, of the revellers are drawn by the daily thrill of being chased through the northern city's streets from a pack of huge, charging bulls.
It's a combination expected to draw more than a million tourists to Pamplona, popularised worldwide by Ernest Hemingway's 1926 novel, The Sun Also Rises.
Party-goers were already drinking copious amounts of alcohol before the official start, squeezed into the main square. Some sat on friends' shoulders. One woman had stripped to the waist.
"I'm here to have fun, to enjoy with the locals and to run with the bulls," said 24-year-old Australian Adam Espron, wearing yellow sunglasses.
Two large glasses of sangria in his hands, Californian tourist David Panijelene was euphoric. "It is the first time for me. Today is my birthday," he said.
The festival's first bull run will be held at 8:00 am (0600 GMT) on Thursday, when hundreds of people race ahead of six fighting bulls and six steers stampeding through an 848.6-metre course from a holding pen to the city's bull ring.
The bull run takes on average just under four minutes, with 2,000 to 3,500 runners daring to get as close as possible without being trampled or pierced by the beasts' horns.
Every year between 200 and 300 participants are injured. Most are hurt after falling but some are trampled or gored by the bulls despite increased safety measures.
The most recent death occurred two years ago when a bull gored a 27-year-old Spaniard to death, piercing his neck, heart and lungs with its horns in front of the hordes of tourists.
This year organisers have launched a free iPhone app in English to help revellers to assess the chances that they will emerge from the festival unharmed.
It asks users about their behaviour at the festival, including how much they have had to drink and how many hours of sleep they have received.
The daily bull runs are the highlight of the festival, which ends July 14, but there is also dancing and drinking, lots and lots of drinking.
In the evening the beasts are killed in the bull ring and their meat is served up in city restaurants.
The city of some 200,000 residents expects the number of people who will take part in the festival this year will be at least as much as last year when 1.5 million people turned out and hotels reported a 95-percent occupancy rate.
The official opening of the festival and the morning bull runs are broadcast live on public television, drawing millions of viewers.