DAHANA-E-AHANGARAN, Afghanistan — The three boys were buried on the southern face of the mountain in May. The side-by-side graves of the brothers Amir Khan and Liaqat are marked with a green flag. Mujtaba’s grave is covered in a rocky mound and light from the morning sun.

It was a Soviet bomb, dropped from an aircraft decades before in 1986, that killed them this spring in Bamiyan Province. The crudely welded silver cylinder, just bigger than a soda can, was one of many others ejected from a cluster bomb as it fell through the sky before resting in a shaded rocky ravine for 33 years.

Accounts of children finding old bombs and accidentally setting them off have become a central part of Afghanistan’s story, horrifying in how frequently it is repeated. The deaths of the boys in Bamiyan, a relative haven from the fighting all around the country, are a particularly cruel example of the hidden dangers in Afghanistan.

War after war, piling on each other for decades, has left Afghanistan covered in more than 1,000 square miles of mines, unexploded munitions, roadside bombs and shuttered firing ranges, according to Afghan government data. Many hazards have been marked, cordoned off, cleared or avoided.