At least 400 people took part on the annual International Pillow Fight Day in London's Trafalgar Square on April 7, 2012. The event started at 3pm and was followed by a clean up by Westminster Council workmen.
A pillow fight is a game in which people engage in mock physical conflict, utilizing pillows as weapons. It looks better when the pillows are filled with feathers that will fly everywhere when the battle will rage, although modern pillows tend to be stronger and are often filled with a solid block of artificial filling, so breakage occurs far less frequently, as this Wikipedia article observes.
On Trafalgar Square, a man particularly drew attention on him as he dressed in the costume of Spider-Man.
The International Pillow Fight Day was organised in more than one hundred cities throughout the world. A website has been set up to list the different events, from London to Panama City or Saigon (Ho Chi Minh City, where it was the first pillow fight ever)