Sixty-eight years ago last week, the atomic bomb blew the roof off of the Kirihawa family's container factory in Hiroshima but left the red brick walls standing. Rising like a Phoenix, the container factory was back in business in three months but the factory relic remained, a constant reminder of the devastation caused by the world's first atomic bomb.

Most people have heard of the Hiroshima Atomic Dome, the skeleton of the building is the centerpiece of the Hiroshima Peace Garden. It has been preserved exactly as it stood on that morning of August 6, 1945 after the atomic bomb burst directly overhead, save for some restoration work to stabilize the dome in case of an earthquake. It was declared a World Heritage Site in 1996.

But the Atomic Bomb Dome is by no means the only surviving building. The bomb devastated about five square miles of downtown Hiroshima totally destroying, about 60 percent of the buildings in that area. But that means that about 40 percent of the buildings survived in various stages of damage.

As Hiroshima rose from the disaster, many of the buildings were razed to make way for progress, yet it began to dawn on the city fathers that Hiroshima was losing some of its atomic-bomb heritage. Since 1993 the city has undertaken to list all of the remaining atomic-bomb buildings, in much the same way as other cities try to preserve their heritage buildings.

Nagasaki, hit three days later, has far fewer surviving relicts of the atomic bomb that hit the city on August 9, 1944 – no iconic building like Hiroshima's Atom Bomb Dome. A city landmark, the Urakami Cathedral, might have served except that it was more heavily damaged and its parishioners insisted that it be rebuilt.

For Nagasaki's large Christian Community, it is as much a symbol of the persecution of Christians in Japan as it was a reminder of the atomic holocaust. They insisted that a new cathedral be built on that spot. The only relic is the old bell tower, which was blown 35 yards away and still rests where it landed.

The main symbol of the atomic bombing in Nagasaki is the large "pointing statue" by sculptor Seibou Kitsamura, and some other sculptures that sit in the middle of the city's Peace Park.

Most of Hiroshima's surviving buildings, like the Kirihara container factory, are hardly architectural gems. They are mostly mundane, workaday buildings whose only intrinsic value is their connections with the atomic bombings, which some fear are fading in memory.

Since 1993 Hiroshima city has generously subsidized private owners who promise to keep their atom-bomb buildings the way they were 68 years ago. However, the owners do not need city approval to tear them down if necessary and the number of such edifices has been gradually shrinking, from 98 registered buildings in 1996 to 86 today.

The current chairman of the materials factory, Shinichiro Kirihawa, 50, told Kyodo News wire that having to tear down the old building was a shame but a business necessity. The company's cardboard box business is booming and it is in dire need of a warehouse. The old factory stands in the way. Kirikawa said he hopes to retain one of the red brick walls as a reminder.

Preserving these bombed-out buildings as "living witnesses" to the atomic holocaust is important to keep memories alive, said Yoshifumi Ishida, who heads the Hiroshima city department that maintains the Atom Dome and other monuments and memorials. He noted that even with government subsidies the plants are expensive to maintain.

Another controversial decision affects the Hiroshima Peace Memorial Museum, which attracts about a million visitors a year and is scheduled for extensive renovation in 2016-2017 including removal of one of the museum's more controversial exhibits.

On entering the museum visitors are treated to a fearsome tableau designed to illustrate the gruesome immediate aftermath of the atomic bombing. It shows the life-size plastic images of three people, an adult woman, a female student and a young boy, clothed in rags, gaping wounds, grim visage, seeming to wander aimlessly through the rubble of the bombed out city.

The museum board decided in March to replace the exhibit with more samples of original artifacts such as burned clothes. The main reason might be that the exhibit is considered too graphic for visitors, especially the thousands of elementary and secondary school children who visit the museum every year. Some say they have had nightmares from it for some years.

Local opposition, however, is growing to save the exhibit. Supporters argue that the atomic bombing was a nightmare in itself and there is no reason to try to prettify what happened.

This year for the second time the US Ambassador to Japan, John Roos, attended the annual ceremony commemorating the anniversary of the bombing. In 2010 he was the first American envoy to do so. Last year he became the first US Ambassador to attend the ceremony marking the August 9, 1945 bombing of Nagasaki.

What municipal leaders in both countries really want is a visit by President Barack Obama. During a press conference in Tokyo during his 2009 visit, The US President said he hoped to be able to visit the two cities sometime during his presidency. He has made two visits to Japan but was not able to fit into the schedule.

Officials of both countries are working to arrange for Obama to visit Japan for the third time, possibly in the spring, and a visit to either or both of the bombed cities may be high on the agenda this time. He would be the first US President to visit either city.

If a 2014 visit is considered too politically risky during an election year, Obama will have one more chance in 2016, when he will be in Japan to attend the Group of Eight summit being held in Japan that year.