Our friend lay in bed, plucking nervously at the gray, bloodstained sheets, her eyes covered by a bandage, her face patterned with glass cuts. “I want to go home,” she said vehemently. “I’m terrified of staying in this building.”

We could understand her concern: the concrete blocks and curved facades of the Kosevo hospital complex in Sarajevo were scarred by shrapnel marks, bullet marks, and shell craters. Two weeks earlier, two patients had been killed when a shell hit their ward. We could hear the sounds of bombardment in the distance, and, suspiciously close to the hospital, the hollow sound of outgoing mortar fire. Hospitals are generally immune from attack under the Geneva Conventions, which grant civilians and civilian objects a high level of theoretical protection in times of war. The siege of Sarajevo, however, made a mockery of the humanitarian ideal that the dangers of war should be limited, as far as possible, to the armed forces engaged in the fighting.

The concept of immunity, the rule that certain people and places should be “protected and respected” during wartime, can be dated back at least to 1582, when a Spanish judge suggested that “intentional killing of innocent persons, for example, women and children, is not allowable in war.” The Geneva Conventions of 1949 confirmed immunity for civilians, hospitals, and medical staff, and the 1977 Additional Protocols to the conventions state: “The civilian population and individual civilians shall enjoy general protection against the dangers arising from military operations.”

The absolute rule is that civilians must not be directly targeted for military attack. Furthermore, some individuals considered especially vulnerable —children under fifteen, the elderly, pregnant women, and mothers of children under seven—are granted special protection and may, for example, be moved to safe zones exempt from attack by agreement of the warring parties. The wounded, sick, or shipwrecked, military personnel who are considered to be hors de combat, are protected, as are prisoners of war.

Hospitals, both fixed and mobile, ambulances, hospital ships, medical aircraft, and medical personnel—whether civilian or military—are also entitled to protection from hostile fire under the Geneva Conventions, provided that structures are marked with a red cross or red crescent and not used improperly or near military objectives, and staff are properly protected. Staff include not only doctors, nurses, and orderlies, but the drivers, cleaners, cooks, crews of hospital ships—in short, all those who help a medical unit to function. Some aid workers—for example, Red Cross volunteers treating the sick and wounded on the battlefield—are also covered, as are military chaplains. Other than hospitals, certain other buildings cannot be attacked. Places of worship and historic monuments are protected, as are civilian structures like schools and other objects that are not being used to support military activities. Under the 1954 Convention on Cultural Property important places of worship, historic sites, works of art, and other cultural treasures are likewise protected from attack.

There are exceptions. A school, for example, becomes a legitimate military target if soldiers are based there. With hospitals, the situation is more complicated since they are permitted to keep armed guards on their grounds. But immunity from attack can be lost if the people or objects are used to commit acts that are harmful to one side in a conflict. If the Bosnian Serbs besieging Sarajevo had concluded that government forces were firing weapons from within the Kosevo hospital complex, they would have had the right to fire back—but only if they had first asked the Bosnian government to stop using the hospital as a shield and had given them a reasonable period to comply.

Causing harm to an innocent person or object is not always illegal. Civilian deaths and damage are allowed as the result of an attack on a military target, but only if the attack is likely to confer a definite military advantage. Damage to people or objects who are in principle deemed to be immune under international humanitarian law must not be excessive in relation to the expected military gain. For example, breaking the windows of a hospital during an attack on an arms dump five hundred meters away would not be illegal since the civilian damage would be far outweighed by the military gain.

But keeping legitimate military targets separate from protected civilian sites is hard to do on the ground. Under international humanitarian law, the parties to a conflict are obliged to separate their military from their civilians as much as possible. But the reality is that this can be difficult. In Sarajevo, for example, the territory under siege was so small that to do so was all but impossible. That said, in Sarajevo, as in many towns across Bosnia-Herzegovina, it seemed clear that the besiegers’ primary target was civilians. That was one of the reasons why Radovan Karadzic and Ratko Mladic, the civilian and military leaders of the secessionist Bosnian Serbs, were charged with war crimes by the International Criminal Tribunal in The Hague.

(See civilian immunity; civilians, illegal targeting of; medical transports; proportionality; protected persons.)