LONDON, ENGLAND - APRIL 21: Runners in the London Marathon pass Buckingham Palace as they enter the finishing straight on April 21, 2013 in London, England. Thousands of runners are taking part - with some wearing black ribbons as a mark of respect to the Boston victims. Extra police are on duty as an estimated 500,000 people line the streets of the capital. (Photo by Peter Macdiarmid/Getty Images)
