Big Ben's famous chimes will fall silent until 2021 to allow essential repair works to take place.
The bongs rang for the final time at midday on 21 August before being disconnected to allow the clock and surrounding tower to be restored.
The Great Bell has sounded on the hour for 157 years. It last fell silent in 2007 and before that, for major refurbishments between 1983 and 1985.
Parliamentary authorities said stopping Big Ben - the commonly used name for the Palace of Westminster's Elizabeth Tower - would protect workers carrying out the repairs. It will still sound for important events including New Year's Eve and Remembrance Sunday.
Big Ben basics
The Great Bell forms part of the Great Clock in the Elizabeth Tower - commonly known as Big Ben
It weighs 13.7 tonnes and the Elizabeth Tower stands 96m (315ft) tall
Every hour it strikes an E note, and every 15 minutes four "quarter bells" chime
To stop the chimes, the striking hammers will be locked until 2021
The landmark Elizabeth Tower is said to be the most photographed building in the UK.
Scaffolding is up and repair work has already started.
The project's principal architect Adam Watrobski told the BBC the repair will install new amenities in the tower, including a lift, toilet and kitchen.
Essential maintenance will also be carried out and the building will be made more energy efficient.
As well as conservation work to the tower, the Great Clock will be dismantled piece-by-piece and its four dials will be cleaned and repaired. The Ayrton Light, which shines when Parliament is sitting, will also be renovated.
During the repair work, an electric motor will drive the clock hands until the main mechanism has been restored, so it will continue to tell the time.
Almost as one, the crowd that had gathered in Parliament Square and on the pavement outside the Palace of Westminster pointed their mobile phones up towards the famous clock. The passing traffic paused, and as the last of Big Ben's bongs sounded - at least until November - cheers broke out.
Most of the people who had taken up Parliament's suggestion to witness the last bells spoke of their sadness at the switch-off, and plenty, like Brian Mignot from Tasmania, questioned the four-year timescale.
"It's a momentous occasion", said one of the onlookers, Annette Nicholson, from South East London.
"I thought the crowd would be even bigger."
Mark Tan, who had just arrived in the UK on holiday from Singapore, said: "It's a historic moment but it's good so that it will continue for another 100 years"
Liberal Democrat MP Tom Brake, a member of the House of Commons Commission, said: "I understand why people would get excited about Big Ben and the Elizabeth Tower and the clock because they are so symbolic and people come from all over the world to have their photographs taken in front of it, and that's why we need to ensure that these works happen to ensure that this symbol of our Parliament, our nation, is available for people to relish for years to come."
In New Palace Yard, 200 parliamentary staff watched the bell bong, with the jocular Labour MP Stephen Pound wiping a tear from his eye. “Bong-o gone-o, that’s so wrong-o,” Pound told reporters as he arrived in the courtyard. As the final bell rang, Pound called the sound “misery in the key of E”.
“This is a desperately sad moment and you don’t know what you’ve got till it’s gone,” he said. “I think it’s the passing of something that means a great deal to a great many people – certainly to my constituents. It’s an elegiac moment of sombre sadness as the bells cease.” Pound said he doubted that the chimes would return on schedule in 2021. “They’re not going to be back in four years. Have you ever known any government project come in on time or on budget?” he said.