Within the span of a day in New York, I paid respects at two memory sites. They commemorated two different sets of events, separated by more than half a century, each murderous and horrifying. Each struggled with what it means to remember – that is, with the ethical obligation of the rememberer.

One, the Face of the Ghetto, an astonishing exhibition of photographs by Jewish photographers in the Lodz Ghetto, turned the United Nations Visitors Center into Jewish memory space. Organized by the German Topography of Terror Foundation – an organization that grew out of imperative to remember and account for atrocities perpetrated by the Nazi SS and Gestapo – the exhibition drew from thousands of archival photos uncovered by the organization’s researchers and was first mounted earlier this year in Berlin. It opened at the UN as part of the UN’s official Holocaust Remembrance Week events in January.

The Lodz Ghetto was the last to be “liquidated” during the Holocaust, when the remnants of its population – those that had not already succumbed to disease and starvation, or been shipped off to death camps – were transported to Auschwitz in the summer of 1944. Its relative longevity was due to the controversial policy of its leader, Chaim Rumkowski, to make the ghetto’s labour force “indispensible” to the German economy. In the end, however, the ghetto was doomed, because the goal of the Nazis was the utter eradication of the Jews.

Rumkowski deployed a cadre of photographers to demonstrate to the Germans the ghetto’s productivity. The photographers went well beyond this mandate, documenting the efforts of the ghetto Jews to normalize their lives under horrifyingly abnormal conditions, and their rapid deterioration despite their best efforts. The accompanying wall boards incorporated lengthy quotations from the Lodz Ghetto Chronicle, so that visitors to the exhibition could see what ghetto inhabitants saw and encounter their words.

But, as Lodz survivor Roman Kent reminded visitors, photographs can’t capture the extreme cold or the stench of the ghetto, nor the pain of parents whose children were taken to their death, nor the courage of the musicians and artists whose insistence on maintaining culture against all odds gave others inspiration and comfort. He called them “messengers of life,” something far more significant than the “gun-carrying messengers of death” bent on destroying them.

Turning the UN into Jewish memory space is significant, not only for what it says about the past, but what it points to in the present and the future. German Ambassador Peter Wittig pointed to the need to take account of a disturbing trend – that “antisemitism is still an issue in many European countries and beyond.” He saw the potential of the photographs to educate young people about the dangers of antisemitism.

The second memorial site I visited, the 9-11 memorial, located at Ground Zero in southern Manhattan, commemorates the victims of the 2001 act of terrorism that brought down the twin towers of the World Trade Center. Unlike the UN exhibition, which brought the memory of a European event to North America, the 9-11 memorial is located on the site of destruction. Rather than depict the events, the memorial uses a more abstract design to convey the tragic loss of human life, and the unspeakable bereavement in its aftermath.

Designed by Israeli architect Michael Arad, the memorial consists of two identical pools, each occupying almost an acre. Each pool is a perfect square, fed by thirty-foot waterfalls on all sides. In the centre is an even deeper pool into which the water disappears. From most vantage points, one can’t see the bottom, giving the impression of an abyss, a void, or an open grave. I thought of the biblical Sheol, and of Jacob’s anguished lament for his vanished son Joseph: “I shall go down to my son mourning unto Sheol.”

As different as they were, both memorials emphasize the same thing: the need to commit to ending hatred. A video at the 9-11 Visitors Center reiterated the themes of unity, loss and building a future free of hate. At the opening of the Face of the Ghetto exhibit, Roman Kent expressed the same sentiment: that the presence of the photographs at the UN “symbolize that humanity all one people living on the planet.”