In October 1961, U.S. tanks near Checkpoint Charlie. (AFP/Getty Images)

In the succeeding months, Allied and Soviet forces continued to jostle over the right of Western diplomats and soldiers to move freely across the line and into East Berlin, a standoff that climaxed with opposing tanks maneuvering for 17 hours on Friedrichstrasse before the Soviet tanks backed away.

On Thursday, to mark the anniversary of a day that some feared would trigger nuclear war, the National Archives National Declassification Center and the Central Intelligence Agency’s Historical Review Program released 370 documents about the building of the Berlin Wall.

One thing those documents make clear: No one in the West saw the wall coming.

The materials are drawn from 11 different government agencies and include intelligence reports, U.S. Army and NATO contingency plans, photographs of the wall rising, and a 600-page State Department analysis covering the situation in Berlin from 1958 to 1962.

The documents “round out our understanding of these events,” said Donald P. Steury, a historian at the CIA. “What they show is that the wall itself was a surprise.”

Over the course of its 27-year life, at least 136 people were killed trying to cross the Berlin Wall. The CIA and the National Declassification Center are planning future releases on “Living with the Wall” and the “Fall of the Wall.”

Before August 1961, the CIA and others had predicted that East Germany would attempt to slow or halt the flow of refugees. Between 1949 and 1961, nearly 3 million people fled the country, which had a population of 17 million. A new pass system or much closer inspections at the border were considered likely scenarios.

In May 1959, for instance, the CIA’s Office of Current Intelligence warned that East Germany, not the Soviet Union, “might restrict traffic at the border crossings to reduce or eliminate uncontrolled access to West Berlin.”

At a conference Thursday at the National Archives in Washington, Hope Harrison, a professor at George Washington University and the author of “Driving the Soviets up the Wall,” said the construction was largely an East German initiative.

“The Soviets resisted this for eight years,” she said, noting that Joseph Stalin, who died in 1953, had first rejected East German entreaties to close the border with West Berlin.

The Berlin Wall was a test of the young presidency of John F. Kennedy. The previous year, at a summit in Vienna, Kennedy was startled by the vehemence of Soviet leader Nikita Khrushchev, who attempted, with some success, to browbeat his American counterpart.

William R. Smyser, a professor at Georgetown University who was a diplomat in Berlin in 1961, recalled at the conference Thursday that after the Bay of Pigs fiasco, Khrushchev believed Kennedy was weak and could be pushed around. “Kennedy is a boy in small pants,” Khrushchev said.

It remains a matter of historical debate whether Kennedy could have prevented the building of the wall by taking a tougher stand with the Soviets. And Kennedy has been criticized for focusing only on the rights of the Western powers not the fate of the citizens of East Berlin. But Smyser, the author of “Kennedy and the Berlin Wall,” said the president received “ghastly” advice from his Harvard-educated Soviet specialists, and ultimately acquitted himself well, keeping West Berlin free while avoiding war.

Smyser said the Berlin crisis was a critical moment in the education of a young president, one that prepared him for the Cuban missile crisis. And he said other young presidents have also been educated by the burdens of command.

“We’re going through it again now,” he said.