This was the brutal crushing of pro-democracy demonstrations in 1989, when troops and police killed several hundred unarmed people around Beijing's most famous square.
The Tiananmen Square protests were sparked by students mourning the death of a liberal Party leader, Hu Yaobang.
Demonstrators soon began to call for greater democracy, an end to official corruption, and even the overthrow of the Party.
The authorities' response was contradictory, reflecting a power struggle under way between reformers and conservatives.
Protests spread across China, and hundreds of thousands of people travelled to the capital to take part.
Worried by the threat of social chaos, hard-liners within the Party leadership got the upper hand, placing the capital under martial law.
But the Square was not cleared, and on 30 May students erected the "Goddess of Democracy" statue, cheered by onlookers.
Finally the Party resolved to act.
On 4 June 1989, on the orders of Deng Xiaoping and other Party elders, troops and tanks of the People's Liberation Army and People's Armed Police cleared Tiananmen Square.
Although the Party claimed nobody was killed on the Square itself, several hundred people were killed by the army and police on nearby streets as the troops lost control and opened fire on unarmed protesters.