A photo exhibit on Boston Common is both weather-proof and, for passersby, like Natalie Gudel, unexpected. The faces of some 70 Holocaust survivors are stretched across massive mesh frames lining the walkway.

“I was just walking through, I had no idea what it was and someone in front of us mentioned that it was Holocaust survivors,” said 27-year-old Gudel. “To me, as a millennial, it seemed like this happened so long ago, remembering that people are still alive from when it took place. They’re survivors and it's impactful.”

"To me, as a millennial, it seemed like this happened so long ago, remembering that people are still alive from when it took place, they're survivors and it's impactful."
Natalie Gudel, Passerby

The larger than life portraits have been on display at the Boston Common for two weeks, but have become especially relevant in the wake of the deadly synagogue shootings in Pittsburgh.

“Maybe we haven’t learned our lesson and I think we start forgetting it,” said Mirko Malik, project manager for exhibit called “Lest We Forget."

"Maybe we haven't learned our lesson and I think we start forgetting it."
Mirko Malki, project manager for 'Lest We Forget'

Artist Luigi Toscano debuted the installation three years in his hometown of Mannheim, Germany, to commemorate the 70th anniversary of the end of World War Two. Since then, it has traveled the world, and at each stop Toscano takes portraits of local Holocaust survivors and adds to the display.

For the Boston exhibit, Tania Lefman was among nine people Toscano photographed.

“When I looked at my picture I kind of fell back. I said, 'my god, look at all the wrinkles,'” said Lefman with a laugh, “because it’s a close up and you can see every expression.”

Lefman is from Poland and, at age 89, remembers vividly when the Nazis invaded in 1939.

“When I think about it, it gives me the chills almost, what I endured in my life,” she said. “I hid underground, in a shallow grave almost, for two and a half years,” she recalled. “It was beyond description, I mean the hunger, the cold, all that.”

"Would you ever believe that our country would have open demonstrations like that? I couldn't believe it would happen ever. But, you see, it can happen anywhere and it starts slowly."
Tania Lefman, Holocaust Survivor

After the war, she and her husband built a life — and a family — in the United States. It was possible she says because of something fundamental to this country: a sense that people are equal. She hopes when passersby see her picture they will consider not just history but how it can repeat.

She points not only to the shootings inside the Pittsburgh synagogue, but also the 2017 “Unite The Right” rally in Charlottesville, Virginia, in which organizers chanted the words “Jews will not replace us”.

“Look what the nationalists, they come out with the neo-Nazis and all that,” she said. “Would you ever believe that our country would have open demonstrations like that? I couldn’t believe it would happen ever. But, you see, it can happen anywhere and it starts slowly.”

The “Lest We Forget” exhibit will be on the Boston Common until November 10.

Correction: An earlier version of this story incorrectly stated that the Nazis invaded Poland in 1941. Poland was invaded in 1939.