It is hard for many of us today to imagine the scale of death and destruction that enveloped Hiroshima when the US dropped an atomic bomb on the Japanese city in August 1945.
The August 6 bombing destroyed 90% of the city. Anyone within a 500 metre radius of ground zero died instantly. The temperature at the drop zone reached 3,000C to 4,000C in the seconds after detonation. Three to six weeks later most of the victims with severe radiation symptoms died.
By the end of 1945, 140,000 deaths were attributed to the bombing and to date the action in Hiroshima is responsible for 300,000 deaths.
On May 27, Barack Obama became the first US president to visit the city since the event - more than 70 years after B-29 Enola Gay dropped the device which was codenamed Little Boy.
The president did not apologise for the actions of his countrymen some 16 years before he was born but offered a carefully choreographed display reflecting on the horrors of war.
"Death fell from the sky and the world was changed," Obama said, after laying a wreath, closing his eyes and briefly bowing his head before an arched monument in Hiroshima's Peace Memorial Park which honours those killed.
The bombing, Obama said, "demonstrated that mankind possessed the means to destroy itself."
"We must have the courage to escape the logic of fear and pursue a world without them," Obama said of nuclear weapons.
As he and Japanese Prime Minister Shinzo Abe stood near the famed bombed-out Genbaku domed building, Obama acknowledged the devastating toll of war and urged the world to do better.
"We stand here in the middle of this city and force ourselves to imagine the moment the bomb fell ... we listen to a silent cry." Obama said.
The visit came after Obama had been with world leaders for the G7 talks in Shima.
Although some 70% of Japanese people backed the visit to Hiroshima, it was not without controversy.
Many in the US see the attacks on Hiroshima and Nagasaki as justified, having hastened the end of the Second World War. They argue that the bombings eliminated the need for a US invasion which would have ultimately cost many more lives.
In contrast others have called it a war crime that targeted civilians.
Obama met and spoke to survivors of the Hiroshima bombing.
He signed the guest book in the memorial park: "We have known the agony of war. Let us now find the courage, together, to spread peace, and pursue a world without nuclear weapons."
Japanese PM Abe said he sincerely respects Obama's courage in deciding to visit Hiroshima. He wants the president's visit to open a new chapter in reconciliation between the US and Japan.