It occurred 50 years ago this month, a story known primarily by people now dead but one that is vital for our times, and for all time. It is a tale about the Pentagon Papers, the Unitarian Universalist Church, a teeny publishing house, a radical historian, a renegade Pentagon employee, a couple of suitcases spilling over with secret documents, a meeting on Boston Common, a few FBI agents, and -- here is the poetry and poignance of it all -- a tourist walk called the Freedom Trail.

And at the center of it all is an enigmatic senator who died at age 91 last weekend.

The senator was Mike Gravel, a two-term Democrat from Alaska and two-time presidential candidate, an idiosyncratic politician who both alienated liberals (for his support for the Trans-Alaska oil pipeline) and delighted them (for reading the Pentagon Papers aloud on the Senate floor), and a central figure in one of the most important political, judicial and press episodes in American history.

It was Gravel who assured that the Pentagon Papers got a thorough airing, arriving one July 1971 day at the Boston offices of the Unitarian Universalist church-affiliated Beacon Press “determined,” as onetime assistant to a Beacon editor Deborah Johansen Harris (who was there when the senator arrived) said in a phone conversation the other day, “to have the entire Pentagon Papers published.”

And it was Gravel who met with Beacon editor-in-chief Arnold Tovell and radical historian Howard Zinn on Boston Common to plan their publishing strategy. The New York Times, The Washington Post, The Boston Globe and 14 other newspapers had published excerpts from the papers, but no major publishing house dared take on the entire project. Soon thereafter, the FBI arrived at the Beacon offices as well; Burnell O’Brien, the secretary to Press director Gobin Stair, bought time by gamely suggesting that the G-men take a stroll on the Freedom Trail, Boston’s walking tour of Revolution-era landmarks, for a half-hour.

The documents in Gravel’s suitcases were a horrific mess, “an endless pile of notes,” according to a Beacon account. They were the raw materials of history, and of a landmark lawsuit, documents like the Oct. 14, 1966, draft memorandum by Secretary of Defense Robert S. McNamara to President Lyndon B. Johnson that said -- in contravention to what the Johnson administration was telling Congress and the public -- of the war in Vietnam, “The prognosis is bad that the war can be brought to a satisfactory conclusion within the next two years. The large-unit operations probably will not do it; negotiations probably will not do it.”

Bombshells like that were in the documents that onetime Pentagon employee Daniel Ellsberg copied and was peddling around Washington, hoping that they would see the light of day so that Americans would see the futility of the war. Neil Sheehan of The New York Times showed interest in the papers -- he and Ellsberg were engaged in a dance of the documents that both found frustrating -- but Ellsberg’s preference was for them to become public off of Capitol Hill.

“Neil did not want the Times to be scooped by Congress,” Ellsberg said in an interview. “He didn’t want Congress to share the glory. He never really understood my motives, to have Congress look into [sitting President Richard] Nixon’s policies, which by the way they never did. Now I realize it was because the hearings would be about the Democrats: how much the Democrats, going back to [Harry] Truman, had lied, especially LBJ. It would have been a political bloodbath for the Democrats, blamed for getting us in the war and then pulling the rug out of the war effort. I thought Nixon would blame Vietnam on the Democrats and then get out. That didn’t happen.”

The war over the papers -- resolved by a Supreme Court ruling in favor of the newspapers and asserting a strong presumption against government-directed “prior restraint” -- has become part of heroic American folklore, sealed by the 2017 Steven Spielberg film “The Post.”

“I was drawn to doing a character study of the moral fiber of [Post publisher] Katharine Graham in her most difficult decision, putting herself in jeopardy and her paper at risk,” Spielberg told me. “Exposing the papers to the Times and then to the Post did not stop the United States from any of its military objectives and didn’t put any soldiers at risk. It was a flashback report, and I always remember the idea that the Founding Fathers gave the free press the powers it must have to do its work and to serve the governed and not the governors.”

But the forgotten strength of character displayed by the Beacon Press never has been celebrated properly.

“I will cooperate with you in your efforts to publish because there is an urgent need for Americans to understand our past errors so that we may exercise informed judgment to end the war in Indochina,” Gravel wrote to Stair, “and because we must begin the process of restoring the people’s faith in their leaders.”

For his part, Stair, who was subpoenaed to appear at Ellsberg’s trial, regarded the publication of the Pentagon Papers as “a test of our purpose.” He said he published the papers out of concern “at how rapidly the American press lost interest in the Pentagon study once the Supreme Court confirmed the public’s right to this information.”

Aside to journalism students: I learned some weeks ago about Gravel’s valises full of documents and his efforts to get the Pentagon Papers published, and vowed to write about it in this 50th anniversary year. But one thing led to another, and one column topic popped up after another, and it wasn’t until last week that I finally was going to get around to calling Gravel, whose telephone number I had acquired in anticipation of working on this very column. Then -- truly as I was playing around in my mind the angle I would take -- I learned that he had died. This column is less rich because of my delay. There is a lesson in here for me in the last years of my career and for you in the first years of yours: Never put off making that phone call.