James Erwin was browsing Reddit on his lunch break when a thread piqued his interest. A user called The_Quiet_Earth had posed the question: "Could I destroy the entire Roman Empire during the reign of Augustus if I traveled back in time with a modern U.S. Marine infantry battalion or MEU?"

The question struck a chord with the 37-year-old Erwin, a technical writer from Des Moines, Iowa, who happened to be finishing a book called The Encyclopedia of U.S. Military Actions (Through Facts on File). Erwin tells PM that he wasn't impressed by other users' early attempts to answer this question, and so, posting under the username Prufrock451, he came up with his own response. Erwin wrote a 350-word short story chronicling the fictitious 35th Marine Expeditionary Unit (MEU), which suddenly disappears from modern-day Kabul and reappears on the Tiber River in 23 B.C. Erwin posted the piece, finished his meal, and went back to work.

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After work, Erwin checked reddit. Thousands of users had read his post and they demanded more. Excited and overwhelmed, Erwin continued submitting pieces of this growing Internet phenomenon. The next day, Los Angeles–based management firm Madhouse Entertainment contacted him about representation. Within the week, after Erwin had put just more than 3500 words to screen, Warner Brothers Studios bought the movie rights.

Erwin's story, which he titled Rome, Sweet Rome, has a cult following among reddit members, its own subreddit on the site, and has inspired fan music and art. But from the beginning, his posts received comments critiquing the accuracy of his conjured tale. Other redditors commented. Historians commented. Marines commented. "You can definitely tell that the story was something that I dashed out on my lunch hour without doing a lot of research beforehand," says Erwin, an encyclopedia writer and two-time Jeopardy! champ. "Any Marine is going to see mistakes in it, and I'm sure if there were Romans around, they'd say the same thing." He plans on doing intensive technical research during the screenwriting process.

So—disregarding troubling questions about time travel and just why some temporally displaced Marines would feel compelled to destroy an empire——could a single MEU destroy the Roman Empire? To sort through the flood of online responses, PM talked to a Roman military expert and found out how the two sides would line up.

Infantry

An MEU typically contains about 2200 troops, along with their artillery and vehicles. According to Erwin's original reddit story (which will be altered for the movie), the Marines are transported back in time with what they have with them, including M1 Abrams battle tanks, bulletproof vests, M4 rifles, and grenades.

The year Erwin chose (23 B.C.) falls in the reign of Augustus, great-nephew of Julius Caesar and considered the first Roman emperor. His legions numbered nearly 330,000 men. They wore heavy leather and metal armor, carried swords and javelins, and operated catapults. They would have never heard the sound of an explosion before. "Obviously, there is a massive difference in firepower," says Roman military expert and author Adrian Goldsworthy. "Not only would Roman armor be useless against a rifle round—let alone a grenade launcher or a .50 caliber machine gun—it would probably distort the bullet's shape and make the wound worse."

Trajan's Column, Rome Getty Images

In the reddit story, however, Erwin said the Marines would not be resupplied with bullets, batteries, or gasoline from the modern world. "There would be no way of obtaining replacements for these supplies in the ancient world," Goldsworthy says. "An average unit of Marines is not likely to be able to make an oil refinery, start generating electricity, or create machine tools to make spare parts for equipment." And even if they could figure it out, it would take many months or even years. So, as soon as the Marines ran out of gas, their tanks would become little more than hunks of metal.

"In the short term and in the open, modern infantry could massacre any ancient soldiers at little risk to themselves," Goldsworthy says. "But you could not support modern infantry. So all of these weapons and vehicles could make a brief, dramatic, and even devastating appearance, but would very quickly become useless. Probably in a matter of days."

Reinforcements

Erwin's reddit story stipulates that no more Marines will come back in time, although they may recruit in the ancient world. The Marines would have to; even at their lowest periods, the Roman Empire could conscript hundreds of thousands of soldiers whenever it wanted.

"A Roman centurion would say 'Let's take 1000 of these guys. Five hundred of them don't come back? Get another 500 guys,'" Erwin says. "Americans have never been very good at sending people out as cannon fodder. Marines are better trained and are much harder to replace. No Marine sees himself as a cog, and no Marine is."

Both sides pride themselves on having competent leaders down to the smallest unit level. Goldsworthy says the battle would depend on who had the better officers. Erwin believes it would be shock and awe versus numbers.

"Marines are the best warriors ever trained," he says. "But they can't fight an endless wave of soldiers. No one can."

Tactics

The Roman legions and Marines are both highly trained with a clear unit structure and hierarchy of command. They emphasize aggression, dominating the opponent, unit cohesion, and being flexible on the ground. "It's easy to arrange people like chess pieces and march them in a direction," Erwin says. "But when you've got basically huge gangs of people going toward each other at knifepoint, it's very hard to maintain a plan. So they have to improvise."

Romans depended on intimidation to psych out their opponents. They marched in unison and appeared as big and conspicuous as possible, overlapping shields to protect each other from attack. But wearing bright colors and lining up straight isn't going to do much good against a unit of Marines, who would be best off attacking guerilla-style while the Romans marched.

One advantage for the Marines: a knowledge of military history. The Marines would know from Rome's history that its legions could be susceptible to ambushes, such as the one that led to their crushing defeat at the Battle of the Teutoburg Forest. The Marines would have serious disadvantages such as navigation, Goldsworthy says. Besides losing all satellite navigation, their modern maps would be practically useless—everything from the course of rivers to the placement of forests would be different. But, at least in their first encounters with the Marines, the Romans probably wouldn't know that.

Getty Images

The key for the Marines would be to stay on the move and avoid getting bogged down in one place. If they stood still, Goldsworthy says, the Romans could easily surround them and then take advantage of their huge numbers advantage. The Romans would probably use a variety of nasty siege weapons on the Marines, such as the scorpion, a large crossbow that rapidly fired long bolts. Romans were also known to cut off opponents from water and food supplies, forcing them to surrender or die.

Who Would Win?

Historian Goldsworthy says the MEU would probably lose in the long term—without the ability to resupply their modern weapons, they simply wouldn't be able to overcome the Roman numbers. However, he says, they could destabilize the Roman Empire, encourage civil war, and initiate regional fracturing. "[The Marines] might discredit the Emperor by defeating the closest army to Rome," he says. "But they would lack the numbers to control Rome itself—with a population of a million or so—let alone the wider empire."

What about in the film? Erwin says he knows the ending, but won't reveal it anytime soon. He's currently on leave from his technical writing job to work on the screenplay full-time. A release date for the film version of Rome, Sweet Rome, or what it will be called, is still unknown.

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