When Alexander the Great died in Babylon in 323 B.C., his body didn’t begin to show signs of decomposition for a full six days, according to historical accounts.

To the ancient Greeks, this confirmed what they all thought about the young Macedonian king, and what Alexander believed about himself—that he was not an ordinary man, but a god.

Just 32 years old, he had conquered an empire stretching from the Balkans to modern Pakistan and was poised on the edge of another invasion when he fell ill and died after 12 days of excruciating suffering. Since then, historians have debated his cause of death, proposing everything from malaria, typhoid, and alcohol poisoning to assassination by one of his rivals.

But in one theory, a scholar and practicing clinician suggests that Alexander may have suffered from the neurological disorder Guillain-Barré Syndrome (GBS), which caused his death. She also argues that people might not have noticed any immediate signs of decomposition on the body for one simple reason—because Alexander wasn’t dead yet.

As Dr. Katherine Hall, a senior lecturer at the Dunedin School of Medicine at the University of Otago, New Zealand, wrote in a 2018 article published in The Ancient History Bulletin, most other theories of what killed Alexander have focused on the agonizing fever and abdominal pain he suffered in the days before he died.

In fact, she points out, he was also known to have developed a “progressive, symmetrical, ascending paralysis” during his illness. And though he was very sick, he remained compos mentis (fully in control of his mental faculties) until just before his death.

Hall argues that GBS, a rare but serious autoimmune disorder in which the immune system attacks healthy cells in the nervous system, can explain this combination of symptoms better than the other theories advanced for Alexander’s death. She believes he may have contracted the disorder from an infection of Campylobacter pylori, a common bacterium at the time. According to Hall, Alexander likely got a variant of GBS that produced paralysis without causing confusion or unconsciousness.

While historians have long speculated over what exactly killed Alexander, Hall suggests he might not even have died when people thought he did.

She argues that the increasing paralysis Alexander suffered, as well as the fact that his body needed less oxygen as it shut down, would have meant that his breathing was less visible. Because in ancient times, doctors relied on the presence or absence of breath, rather than a pulse, to determine whether a patient was alive or dead, Hall believes Alexander might have been falsely declared dead before he actually died.

"I wanted to stimulate new debate and discussion and possibly rewrite the history books by arguing Alexander's real death was six days later than previously accepted,” Hall said in a statement from the University of Otago. “His death may be the most famous case of pseudothanatos, or false diagnosis of death, ever recorded.”