Cyclists stopped traffic and laid down in the road next to coffins outside Transport for London's (TfL) headquarters in a call for it to spend more money on cycling infrastructure in the capital.
Members of Stop Killing Cyclists blocked Blackfriars Road in south London for 15 minutes on Friday evening after placing 21 coffins outside the TfL office to represent the number of people killed riding bikes in the city since the action group formed in November 2013.
The group was launched after six cyclists were killed that month.
Nicola Branch, co-organiser of the No More Coffins event, said: "We want 10% of the TfL budget to be spent on cycling infrastructure. At the moment it is only 1.4% of their transport budget and that's nowhere near enough.
"Even 10% is a fraction compared with cities like Copenhagen and Amsterdam.
"If you increase the amount of money that is spent on the cycling infrastructure that means that more people will cycle, that means that less people will use private cars.
"As cyclists we are the canary in the coalmine, you sort out the problem of cycling deaths first and then all the other deaths fall into place."
Next to the 21 coffins was a tombstone dedicated to an estimated 24,000 traffic-related deaths in the last three years from issues including pollution and physical inactivity.
At a rally before the protesters laid down, Scarlett Brady-Hughes, eight, poignantly read out the names of the 21 cyclists killed.
Speakers including cyclists who have been hit by HGVs on the capital's roads shared their stories.
Vicky Lebreck, 25, from London, had her leg amputated after her pelvis was crushed by a lorry in December last year, and she fought back tears as she shared her story.
Ms Lebreck said: "I don't think it should be a possible outcome that a mistake made by a driver means people cycling on London's roads should be dying or having dramatic injuries.
"What has happened to me is life-changing. I am trying to get my life together and get used to not being able to do the things I could before."
Eight cyclists have been killed on London's roads this year - six of them were women and seven involved HGVs.
The event was the third annual November protest staged by Stop Killing Cyclists.