Assaults on hospitals have become part of a widespread warfare strategy, propelling numerous actors to claim that belligerents are not being held accountable for attacking medical units. Acknowledging that international humanitarian law (IHL) offers medical units protections, belligerents often claim that the hospitals were being used to shield military targets and therefore the bombing was legitimate. Tracing the history of hospital bombings alongside the development of legal articles dealing with the protection of medical units, we show how, from the early 20th century, international law has introduced a series of exceptions that legitimize attacks on hospitals that were framed as shields. Next, we demonstrate that the shielding argument justifies bombing hospitals because they have ostensibly assumed a threshold position in-between the two axiomatic poles informing the laws of war – combatants and civilians. We argue, however, that medical units tend to occupy a legal and spatial threshold during war and, since IHL does not have the vocabulary to acknowledge the liminal nature of medical units and identifies between liminality and criminality, it introduces several exceptions that help belligerents legitimize their attacks. By way of conclusion, we maintain that the only way to address the deliberate and widespread destruction of medical units is by reforming the law through the introduction of an absolute ban.