Many people mark September 11, 2001, as the day life in the United States became much more tense and frightening than before.
We suddenly became aware of angry people willing to fly jetliners into buildings and others plotting to blow themselves up inside subway tunnels.
But people over a certain age will remember another time that was at least as unsettling.
Fifty years ago, 800 people attended the opening of the Modern Living Show at the Lewiston Armory.
According to Tuesday's "Looking back" column, one display featured a concrete bomb shelter set up to show visitors how to build one in their home or office for "maximum protection."
Public buildings, meanwhile, were outfitted with food, water and signs labeling them civil defense shelters. Children practiced how to "duck and cover" beneath their school desks, and warned they would be blinded if they looked at the nuclear explosion on the horizon.
That threat, of total nuclear warfare, has receded over the years, thanks to efforts begun by President Ronald Reagan to steadily reduce nuclear missiles and warheads.
Unfortunately, it has been replaced by a variety of new threats to domestic security.
We never thought the Cold War would end, just as we now believe we may live with the threat of terrorism forever.
But the world changes. Sometimes slowly. Perhaps one day airport screenings will seem as anachronistic as the old black and yellow "Fallout Shelter" signs.