In an era of “fake news,” “alternative facts” and other assaults on the very idea of truth, you would expect the National Archives — devoted to the preservation of the nation’s history — to be at the forefront of those pushing back. “The National Archives and Records Administration (NARA) is the nation’s record keeper,” the government agency proudly announces on its website. How utterly depressing it was, then, to discover on Friday that the Archives had gone into the business of altering history.

And how reassuring to read the Archives’ forthright — and, for Washington, extraordinary — statement on Saturday: “We made a mistake. ... We have removed the current display. ... We apologize.”

The Post’s Joe Heim reported Friday that the Archives made numerous alterations to a photograph included in an exhibit dedicated to the 100th anniversary of women’s suffrage. The photo shows the massively attended Women’s March held in January 2017 to protest President Donald Trump’s inauguration. But Archives curators altered signs being carried by the women to delete references to Trump — and thereby they seriously distorted the meaning of the event. “A placard that proclaims ‘God Hates Trump’ has ‘Trump’ blotted out so that it reads ‘God Hates,’ “ The Post reported. But “God Hates” was not the message of the protester carrying that sign. Another sign that reads “Trump & GOP — Hands Off Women” has the word ‘Trump” blurred out.

In their initial weak defense, Archives officials noted that they had not altered articles they preserve for safekeeping, only a photograph for a temporary exhibit. We did not find that reassuring. Photo alteration long has been the preserve of authoritarian governments, most famously Soviet dictator Josef Stalin, who erased comrades from historical photographs one by one as he had them executed.

The United States government should never play the same game, even on a small scale. The goal in this case may have been not to irritate the snowflake in chief residing up Pennsylvania Avenue from the Archives. After all, the Women’s March harks back to one of the foundational lies of the Trump presidency, when he falsely insisted, and insisted that his officials likewise falsely insist, that his inauguration crowd was the largest of all time. Trump’s refusal to back down then set the pattern for his presidency: Lies are acceptable, and evidence can be ignored.

Rather than remind anyone of such unpleasantness, the Archives chose to falsify history and pretend that the Women’s March had nothing to do with Trump. That offered a terrible lesson to young visitors to the exhibit about how democracies deal with news, with history — with truth.

Now the Archives has presented a far more uplifting lesson. Admitting and correcting a mistake are usually a lot harder for any of us than erring in the first place. But in their statement, officials did not flinch. The Archives will replace the altered image “as soon as possible with one that uses the unaltered image. We apologize, and will immediately start a thorough review of our exhibit policies and procedures so that this does not happen again.”

Good for them.