Why to go: Judaism, except for a brief time in the first century A.D. when it made converts among the upper classes in Alexandria and Rome, has never been a missionary religion. For that reason, there have never been that many Jews in the world. The most of them that have ever lived at one time are living now in the 21st century: 16 million people.

In contrast, Christians number 1.8 billion, Muslims another 1 billion, Hindus 800 million and Buddhists 350 million.

It is easy to see that Judaism has a far narrower margin for survival than the other great religions. Jews’ traditional status as outsiders in both the Christian and Muslim worlds, as well as their fierce adherence to their identity and beliefs, has often resulted in persecutions, pogroms and institutionalized anti-Semitism. None of those, of course, was as depraved or as deadly as the Nazis almost successful attempt to murder all of the Jews in Europe. The 6 million Jews who died there in the Holocaust between 1941 and 1945 were half of all the Jews on earth.

The Nazis’ single-minded pursuit of the extinction of the Jews reached its self-destructive height near the end of WWII. Obedient functionaries like Adolph Eichmann diverted crucial supply trains from delivering urgently needed arms to the Wehrmacht’s collapsing eastern front to the task of delivering Jews to the death camps. Here the fanatical desire to commit genocide exceeded even the desire for self preservation.

After the establishment of the Jewish state of Israel in 1948, its leaders vowed that “never again” would a Holocaust victimize the Jewish people. They knew that part of honoring that vow would be to keep alive the memory of the people who had perished at the hands of the Nazis and their fascist allies. They knew that as time went on there would arise debunkers and skeptics who would claim the Holocaust never happened or was far less important or severe than reported.

So, in 1953 the Israelis built a memorial, Yad Vashem, in Jerusalem. The site is not a single monument or structure so much as an ensemble of buildings and spaces designed to impart some small understanding of a crime that the human mind cannot ever really grasp. Perhaps the most compelling part of the site is the Hall of Names, where photos of the dead and written remembrances of them by Holocaust survivors are enshrined to give each victim a face and a name. As Holocaust survivors die, and their memories with them, Yad Vashem’s task of finding the names of all who died and remembering something about them becomes hurried and even more poignant.

Even more Jews would have died if there had not been, among other rescuers, “Righteous Gentiles,” non-Jews who sheltered and defended Jews from the fascists, often at the cost of their own lives. They ranged from illiterate French peasants, Danish fishermen and Belgian nuns to powerful men like Swedish diplomat Raoul Wallenberg and the German industrialist Oskar Schindler. They hid and fed Jews, and often gave them false identities and tried to find ways to deliver them to safety in neutral countries like Switzerland and Sweden. At Yad Vashem, sites such as the Avenue of the Righteous Among the Nations and the Garden of the Righteous honor those gentiles

What to add to the journey: This is not a good time to travel to Jerusalem.