The "Lest We Forget" exhibition features 200 photographic portraits of Jewish, Sinti, and Roma people as well as others persecuted under the Nazi regime. The works have been on display in the center of Vienna since early May. During the night following the European elections, unknown assailants attacked some of the images.

German-Italian photographer and exhibition organizer Luigi Toscano spent over a year meeting with Holocaust survivors living in the US, Germany, Ukraine, Israel, and Russia. After the attacks, he expressed his dismay with a post on Facebook, asking: "Austria, what's wrong with you?"

Only a few hours after the crime, several organizations, including Muslim Youth Austria, launched a campaign to repair and protect the series. Volunteers were able to sew the damaged works back together within a few hours.

The efforts of the rescue operation are impressive: Now the only traces of the damage that remain are red stitches. But even before this incident, the exhibition had been attacked two times. Two days after the launch, several photos were slashed with a knife but the damage was not as great.

The images, which have been installed in public squares and parks in 13 cities worldwide, will now be guarded around the clock in Vienna. Several Viennese Muslims are attending the night vigils. In the Islamic holy month of Ramadan, they want to do something good for their community. It is also an opportunity to break the fast together.

Until the exhibition finshes at the end of the month, young Muslims, as well contemporaries from the Catholic Caritas organization and the nesterva artists' collective, want to stay on site to protect the pictures. Mayor of Vienna, Michael Ludwig (3rd from right) also attended the vigil. He thanked the helpers and spoke of a "beautiful sign of civil society."

The head of the Young Caritas, Alice Uhl, is torn. On the one hand, she is overwhelmed by the outpouring of assistance but on the other hand, she is ashamed that the portraits were defaced: "The exhibition has never been attacked so often — and damaged so badly — as it has been in Austria. It is unacceptable! It's important to me that we're here together to take a stand against this."

At least one good thing has come from the attacks: The exhibition is now attracting more and more visitors because of the vigil guarding it, and the media presence. Toscano is looking ahead to the exhibition's next venues. The series of portraits have gone on display in public spaces in Berlin, Ukraine, and the US.

A huge field of stelae in the center of the German capital was designed by New York architect Peter Eisenmann. The almost 3,000 stone blocks commemorate the six million Jewish people from all over Europe who were murdered by the Nazis.

Designed by German artist Gunther Demnig, these brass plates are very small — only 10 by 10 centimeters (3.9 x 3.9 inches). They mark the homes and offices from which people were deported by the Nazis. Around 10,000 of them have been placed across Berlin.

Several high-ranking Nazi officials met in this villa on the Wannsee Lake in January 1942 to discuss the systematic murder of European Jews, which they termed the "Final Solution of the Jewish Question." Today the house is a memorial that informs visitors about the unimaginable dimension of the genocide that was decided here.

White roses on track 17 at Grunewald station remember the more than 50,000 Berlin Jews who were sent to their deaths from here. 186 steel plates show the date, destination and number of deportees. The first train went to the Litzmannstadt ghetto (Lodz, Poland) on October 18, 1941; the last train to the Sachsenhausen concentration camp on January 5, 1945.

Today, the Hackesche Höfe in Berlin Mitte are mentioned in every travel guide. They are a backyard labyrinth in which many Jewish people lived and worked — for example in the brush factory of the German entrepreneur Otto Weidt. During the Nazi era he employed many blind and deaf Jews and saved them from deportation and death. The workshop of the blind is now a museum.

The heart of Berlin's fashion metropolis once beat here. A memorial sign made of high mirrors recalls the Jewish fashion designers and stylists who made clothes for the whole of Europe at Hausvogteiplatz. The National Socialists expropriated the Jewish owners. Berlin's fashion center was irretrievably destroyed during the Second World War.

Before the Holocaust, 173,000 Jews lived in Berlin; in 1945 there were only 9,000. The monument "Der verlassene Raum" (The Deserted Room) is located in the middle of the Koppenplatz residential area in Berlin's Mitte district. It is a reminder of the Jewish citizens who were taken from their homes without warning and never returned.

Architect Daniel Libeskind chose a dramatic design: viewed from above, the building looks like a broken Star of David. The Jewish Museum is one of the most visited museums in Berlin, offering an overview of the turbulent centuries of German Jewish history.

There are still eight remaining Jewish cemeteries in Berlin, the largest of them in the Weissensee district. With over 115,000 graves, it is the largest Jewish cemetery in Europe. Many persecuted Jews hid in the complex premises during the Nazi era. On May 11, 1945, only three days after the end of the Second World War, the first postwar Jewish funeral service was held here.

When the New Synagogue on Oranienburger Strasse was first consecrated in 1866 it was considered the largest and most magnificent synagogue in Germany. One of Berlin's 13 synagogues to survive the Kristallnacht pogroms, it later burned down due to Allied bombs. It was reconstructed and opened again in 1995. Since then, the 50-meter-high golden dome once again dominates Berlin's cityscape.