Remembering the deaths of 4 June 1989 is no neutral task. It is a civic duty, a burden and an act of resistance in countering a state-level lie that risks spreading far beyond China’s borders.

On that day the Communist party sent tanks to clear protesters from Tiananmen Square in the centre of Beijing, killing hundreds of people, maybe more than a thousand. In the intervening years, China has systematically erased the evidence and memory of this violent suppression using its increasingly hi-tech apparatus of censorship and control.

We know this first-hand: one of us was present in Beijing in 1989, while the other wrote a book on Tiananmen’s legacy. Neither of us ever intended to become an activist, yet to broach the subject of 4 June publicly is to challenge the Communist party’s silence and counter Beijing’s attempts at excising this episode from history. Journalists generally shy away from taking political or ideological positions and yet, since China has for 30 years tried to deny its crime, the simple act of writing about it unwittingly tips us into activism.

Separately, we’ve witnessed the success of Beijing’s Great Forgetting. At public talks and in private conversations, we’ve been present at that split second when an eyewitness to the crackdown suddenly realises how their memories have been manipulated. We’ve both seen that moment of shock and discombobulation and heard various versions of the same statement: “I was there. I saw it with my own eyes. But I haven’t talked about it for so long that I’d put it out of my mind. Until this moment, I literally forgot I had been there.”

We only realised the extent to which we too had internalised Chinese censorship when we began to discuss the sense of transgression we felt in broaching so taboo a topic. We experienced this separately over more than two decades, showing how successful the party-state has been in pathologising reporting on Tiananmen, seeding self-regulating, self-censoring mechanisms, even among foreign journalists.

Facebook Twitter Pinterest Beijing’s Forbidden City was the imperial palace until the end of the Qing dynasty in 1911. Photograph: Dan Chung/The Guardian

For one of us, the need for secrecy when writing a book on Tiananmen was so all-consuming that it led to a series of protocols, including never discussing it at home, in the office, by email or on the telephone. These moves were necessary to protect sources, many of whom had already been penalised for continuing to publicly remember. One interviewee, Tiananmen Mothers co-founder Zhang Xianling, said she had once managed to hold a small act of remembrance at the spot where her 19-year-old son, Wang Nan, had died from a bullet to the head. The next year, a closed-circuit camera had been trained on that spot, designed to prevent any public act of remembering.

This leads to a conundrum: how to remain detached and objective when the topic is politically charged? This dilemma is becoming increasingly widespread among journalists and academics, with whole fields of study being pushed into activism by Beijing’s coercive actions. A case in point are the Xinjiang scholars: with one million Uighurs held in political indoctrination camps in the north-west, these academics studying a once obscure speciality have become some of the loudest voices advocating for the Uighur community. For them, activism is not just a moral duty but a professional responsibility, since the culture to which they have devoted their scholarly lives risks being annihilated by Beijing’s assault.

In recent years this dynamic has not been confined to hot-button topics alone, as China retrofits its history into a vision that starts in the stone age and ends with the Communist party, a single continuum that serves to legitimise the current leadership and its narrative of the past, the present and the future.

Beijing is not alone in this exercise of manipulating history. But we are witnessing with China an attempt to write a whole civilisation into the linear history of a single nation. The state is using archaeological finds dating back as far as 2.12m years to stake a greater claim over the history of early human development, foregrounding research that suggests that human ancestors left Africa for China earlier than previously assumed.

The debates can get arcane and heated – for instance, scholars working inside China have been funded by the state to prove the existence of a mythological dynasty called the Xia (presumed dates 2070 to 1600BC). Despite its antiquity, Beijing has invested heavily in researching this era: the Xia-Shang-Zhou chronology project, launched in 1996 and involving 200 scholars, underpins the state’s narrative of 5,000 years of uninterrupted civilisation. It’s a project that has been widely criticised as unscientific and politically driven, by both Chinese and western scholars working outside China.

Facebook Twitter Pinterest A vocational skills education centre in Dabancheng, in Xinjiang province: one million Uighurs are being held in similar camps. Photograph: Thomas Peter/Reuters

With politics firmly in command over history, almost every aspect of China’s past risks becoming a battlefield. In recent years US scholars researching the history of the last imperial dynasty, the Qing (1636-1911), have been vilified by state-run Chinese newspapers for historical nihilism and imperialism. This is because their close examination of how the Qing came to conquer Xinjiang, Tibet, Mongolia and Taiwan ultimately invalidates China’s assertions that all areas under its control are “inalienable parts of China” since time immemorial.

In this way, political no-go zones are scattered throughout the long millennia of Chinese history and scholars lament how much access to archives is being restricted, in particular for topics still little explored, such as the actions and fate of Chinese collaborators of Japanese invaders during the Second World War or issues that touch upon ethnic tensions, whether in inner Mongolia or Tibet.

As if to underline the pitfalls, legislation protecting state-approved heroes and martyrs has entered into the civil code. Probing the past has become a dangerous occupation in the People’s Republic of China and, increasingly, China’s ideological historiography and imposed silences are extending overseas, turning foreign historians into activists.

If events that happened centuries ago are this controversial, imagine how perilous it is to walk the censored days of that Beijing spring just 30 years ago. In this climate, where silence is acquiescence, speaking of forbidden histories becomes a moral choice.

• Louisa Lim is the author of The People’s Republic of Amnesia; Tiananmen Revisited and a senior lecturer at the University of Melbourne. Ilaria Maria Sala is a writer and journalist based in Hong Kong, whose forthcoming Italian book Pechino, 1989 is a collection of her photographs of 1989.