The earliest recorded cases of post-traumatic psychological symptoms have emerged on 4,000-year-old clay tablets from Iraq.
Psychologists have found descriptions of two instances of civilians suffering intense fear, horror, nightmares and sleepless nights in the wake of brutal attacks on their city.
These constitute the first documented evidence of the psychological impact of warfare in recorded history. They also reveal that the Sumerians, builders of the world's first urban civilisation, had a good understanding of the causes of such symptoms.
Menachem Ben-Ezra, a PhD student at Tel Aviv University, in Israel, said his reading of the tablets suggested that the psychological reaction to trauma is biological in nature. He added: "Hence the core symptoms of post-traumatic reaction will be universal and not culture-bound."
Mr Ben-Ezra studied cuneiform tablets excavated in the 20th century from the ruins of the Sumerian city of Ur.
One describes the reaction to the death in battle of King Urnamma in 2094BC and the destruction of Ur. It says: "Evil came upon Ur... They weep bitter tears in their broad squares where merriment had reigned. With their bliss having come to an end, the people do not sleep soundly."
A second chronicles the sacking of Ur by the Ilamites and Subarians 90 years later. It concludes: "The storm's cyclone-like destruction - verily its terror - has filled me full. Because of its (affliction)I in my nightly sleeping place verily there is no peace for me."
Mr Ben-Ezra said the Sumerian descriptions of anxiety and sleep disturbances were akin to what is described today as post-traumatic stress disorder. "The symptoms haven't changed over millennia and exist in traumatised people regardless of gender, race, age or religion," he said.
The research, published in the journal Stress and Health, overturns findings of previous studies suggesting the earliest descriptions of post-traumatic symptoms are to be found in Samuel Pepys' description of the fire of London in 1666. Others have picked out Achilles' agitation at the death of his friend Patroclus in Homer's Iliad, and Odysseus fretting during a storm in the Odyssey.