It was a bomb so big that the USSR wasn't sure that it could test it. The Tsar Bomba, commissioned by Nikita Khrushchev to enhance the Soviet strategic position in the race for nuclear weapons, remains the most powerful atomic bomb ever exploded.
The video above explains how it came to be, and the consequences of its testing.
On the 100th anniversary of the Russian Revolution, BBC Future is running a video series about the influence of the Soviet Union in science and technology.
Read more: The monster atomic bomb that was too big to use
Soyuz: The Soviet marvel that remains on duty after 50 years
MiG: The Soviet warplanes the West feared most
Video by Howard Timberlake and Jose Luis Penarredonda.