Back in the late 19th century, victims of railway accidents began to experience a host of inexplicable symptoms that doctors simply could not make sense of. No one was sure what, exactly, caused the onset of these strange symptoms that had never been seen before and that only seemed to appear after a rail accident. But one doctor, Sir John Eric Erichsen, came up with a name for it: railway spine.

After a series of train crashes in Great Britain in 1867, many victims came forward to claim that they had suffered long-lasting effects that included a variety of symptoms. Some of them were purely mental. Others had physical manifestations, some of which couldn’t be traced to an identifiable source. Among other symptoms, these people were complaining about:

Loss of memoryPoor concentrationSleep disturbancesAnxietyIrritabilityBack painHeadachesHearing problemsNumbness or pain in their extremitiesLack of sexual desire or impotenceBladder disturbances that resulted in frequent urination or a complete cessation of urination, leading to deathParaplegia

The problem was, there was no way to really verify these claims, since medical science at the time was limited largely to what doctors could see. And they couldn’t see anything wrong with these victims—there was no obvious spinal injury, and traditional concussion symptoms were known to disappear after a while. But these people were reporting injuries for years.

The railroads called bullshit. They said these people were just malingerers who wanted money. John Eric Erichsen coined the term and wrote a whole book about these people. The craziest part was, some of the folks complaining of physical or mental problems were witnesses. They hadn’t even been in the crash.

For years, railway spine was a matter of hot debate. Erichsen firmly believed that this syndrome was a physical one that resulted from what we would today see was whiplash, or the sudden backward and forward thrust of the head associated with a sudden change of inertia. He tried to link it to the brain and the spine.

Other doctors of the era, like neurologist Jean-Martin Charcot, considered railway spine to be a traditional case of hysteria—at the time essentially defined as the nervous instability of people, mostly women, who were generally associated with some kind of moral failing. Basically, he was arguing railway spine was a weird, wholly mental syndrome that occurred in people who were, say, sexually unsatisfied, promiscuous, prone to drinking, or simply just had a uterus. In other words, no actual spinal injury was involved.

Seems weird, right? But what these people were experiencing was what today we’d call post-traumatic stress disorder, which is a state of being that occurs after a person undergoes an event for which they are not equipped. That includes tons of things: sexual assault, proximity to war, witnessing a murder, or experiencing a natural or manmade disaster like a railroad accident.

Today, we know that PTSD manifests itself in a ton of really confusing ways. There are mental symptoms like forgetfulness and insomnia. There are physical manifestations like stomach pain or headaches. There are emotional symptoms like depression or inexplicable rage. That’s because a traumatic incident overwhelms a person and even goes so far as to on the brain surface that in turn rewire its functioning. So while a formerly happy soldier may return from war prone to drinking and fits of anger, it’s not because he suffered a concussion: the primal fight-flight-or-freeze instincts so overwhelmed his brain function that it changed who he is.

Interestingly, the appearance and impact of PTSD can often be predicted, with people who have suffered previous traumas being more likely to adopt symptoms, according to psychologist Robert Scaer. Using that logic, it makes sense that so many ‘hysterics’ were women: Freud found evidence of such of girls of the era that it would have caused societal upheaval. He ended up writing those findings out of the published theories we know him for now—but it’s certainly feasible that a woman who had been abused in childhood would have “gone crazy” in adulthood when reintroduced to the sexual realm.

It took a long time to reach that conclusion. We had to cycle through terms like hysteria, soldier’s heart, irritable heart, shell shock, battle fatigue, combat stress reaction, anxiety reaction and more before we reached the term “post-traumatic stress disorder” in 1980. It took further years to take a neurological scan to prove that brain function was dramatically changed in PTSD victims. PTSD has probably always existed as long as humans have been on earth, but its workings are still so mysterious that doctors and psychologists are still figuring it out.

Railway spine, though, is often credited as one of the first major attempts at defining this strange syndrome, and it’s the one that got doctors all around the world studying it. It’s the reason we ended up with Charcot’s theories, which earned him students among the likes of Pierre Janet and Sigmund Freud—two of the men whose work still influences psychology today. And without all of that, we wouldn’t have come to the arrival of PTSD. Even in its most tragic moments, transportation has taught us a hell of a lot.