BUGESERA, Rwanda — It looks like an ordinary church: a neat brick structure with white trim; well-maintained grounds surrounded by a white iron fence. Across the street, children in uniform spill out of a Roman Catholic school in the late afternoon. Another Catholic church has been built nearby.

The calm and order of Nyamata Parish Catholic Church provides no hint of what it holds. The open gate and walkway lead to the front of the church, now turned into the Nyamata Genocide Memorial. A soft-spoken guide welcomed us. He began by explaining that long ago the only distinction between the Tutsi and Hutu tribes in Rwanda was the number of cattle they owned. Competition for power supplanted that distinction; violent conflicts between the two punctuated Rwandan history since the late 1950s. Nonetheless, many Tutsi and Hutu continued to live as neighbors and even friends for much of the time.

In April 1994, everything changed. The genocide began.

Thousands of Tutsis and moderate Hutus sought refuge in the Nyamata Parish church here in Bugesera, a district in Eastern Province in which Nyamata is the capital. Some 10,000 people were slaughtered in the church and the surrounding grounds in days, from April 14 to 19, by Hutu militia. The genocide took place across the country but the Bugesera district experienced one of the highest levels of violence and devastation nationally. From a population of 62,000, only 2,000 survived there.

Today, rows of benches for worshippers, laid out in a semicircle facing a simple altar, are covered in layers of clothing meant to evoke the victims — young and old men, women and children. More piles of clothing rest on the floor at the back of the sanctuary. Bullet holes are visible in the ceiling and in the walls. Blood stains the altar. A few people hid in closets and cupboards but most were killed by machete. How could this have happened? One struggles to breathe.

A ladder leads to the crypt. There, on layers of shelving from floor to ceiling, skulls of all sizes are carefully laid out in rows, some with teeth and some without. On other shelves, bones of the victims are gently arranged.

The crypt is not large enough to preserve the bones and skulls of the thousands of victims from the massacre. About a dozen long rectangular tombs have been created behind the church to provide a final resting place for their remains. I descended a ladder in the one tomb open to visitors. In the dark, the guide’s small flashlight and the light from my phone revealed skulls and bones laid out on shelving with the same care displayed in the crypt. Multiplying these images by the number of tombs and the scale of the barbarity in this one setting, I began to register the atrocity in a way that statistics could not convey.

The peace and quiet of the memorial today stands in sharp contrast to the screams, sobbing, shouts of disbelief and terror that echoed throughout the neighborhood more than 20 years ago. And so the memorial gives form to the unfathomable, and its understated dignity makes the crimes against humanity in the church all the more horrifying.

When leaving the museum, visitors are invited to sign and comment in a guest book. What to write? Words seem banal and inadequate to capture the emotional impact of the memorial and the enormous gratitude I feel for how the genocide was memorialized.

I have been to Dachau and to Auschwitz, and now Nyamata. The message from these memorials is urgent in a world where ethnic and religious hatred is once again being manufactured by unscrupulous leaders. Somber pledges of “never again,” regularly intoned by prominent leaders since the Holocaust, provide no guarantee.

Cambodia, Rwanda and Srebrenica provide evidence of recurring horrors. So, we must heed the warnings of the dead: under certain circumstances, friends and neighbors can be incited to turn on one another with unspeakable brutality; civility must be nurtured and protected because the line between civility and barbarism remains tenuous at best.

Ann Phillips

Ann Phillips is an independent analyst and practitioner with extensive experience working on issues of foreign assistance, specializing on fragile states, conflict, stabilization and reconstruction and system transitions. She is currently a senior adviser to the Academy for International Conflict Management and Peacebuilding at the Washington-based US Institute of Peace, focusing on civilian-military relations.

From 2012 to 2013, Phillips was a public policy scholar at the Woodrow Wilson International Center for Scholars, affiliated with the Africa-Leadership and Institutional Capacity Building program. Before that, she was director of the Program for Security, Stability, Transition and Reconstruction at the George C. Marshall European Center for Security Studies in Garmisch, Germany. She was a professor of international relations and comparative politics from 1986 until 2000, first at Smith College in Northampton, Mass., and then at American University in Washington. She also worked in the Policy Bureau of the US Agency for International Development (USAID).

Phillips has a Ph.D. in international relations and political economy from Georgetown University and a master’s degree in international affairs from the School of Advanced International Studies at Johns Hopkins University.