London was grayer than usual Tuesday as it marked the 10th anniversary of the worst terrorist attack in recent British history. On July 7, 2005, bombers linked to al Qaeda set off explosions on three London Underground trains and one bus. The explosions killed 52 people and injured more than 700.

Survivors and victims' families attended a memorial service Tuesday at St. Paul's Cathedral in London, the BBC reported. The tribute culminated with a moment of silence, petals falling from the church's dome and four lit candles representing the bombing sites.

During the bombings, St. Paul's dome symbolized Londoners' unity, so it naturally became the message of the service.

"Beyond the numbing shock of what happened, there was solidarity. There was unity in our grieving," Richard Chartres, the Anglican bishop of London, said in his address.

Even the bustling London transportation services dedicated time to memorialize victims. People laid flowers at the four bombing sites and held moments of silence at 8:50 local time, when the first explosion occurred 10 years ago.

A "walk together" campaign urged commuters on buses on trains to get off one stop early and travel together by foot. The #walktogether hashtag trended on Twitter, with users posting tributes throughout the day. London traveler Adrian Luscombe, tweeted, "A commuter today as I was 10 years ago. It could have been me. As fresh in memory as if it was yesterday."

The 7/7 Memorial in Hyde Park held multiple services. Prince William attended a ceremony with ambulance and firefighters working during the bombings and victims' families. Through songs and readings, the service memorialized those killed by the blasts.

Another service centered on silent remembrance. Mourners placed more than a dozen wreaths on the memorial's 52 pillars — representing each victim. Prime Minister David Cameron and London Mayor Boris Johnson were among those laying wreaths.

Cameron told BBC that the July 7 was "one of those days where everybody remembers exactly where they were when they heard the news."

Johnson left a note on the wreath, reading: "Ten years may have passed, but London's memory is undimmed. We honour again today the victims of 7/7. You will live forever in the hearts of the people of this city."

Emily Leayman is an intern at the Washington Examiner