Eighty years ago this week, the U.S. dropped an atomic bomb on Hiroshima, Japan on Aug. 6, 1945. Three days later, another fell on the city of Nagasaki. Between 120,000 and 220,000 people died in the blasts or from burns, other wounds and radiation exposure over the next few months.

Groups around the world will gather this week to commemorate the August 1945 bombings of Hiroshima and Nagasaki.

Preparations were underway in Japan’s Hiroshima on Tuesday, just one day of ahead of a major memorial ceremony marking 80 years since the atomic bombing of the city.