An article here describes how a Redditt discussion of how a unit of US Marines would fare against the armies of ancient Rome has been picked up for a film treatment (which doesn't necessarily mean it will get made).
This isn't actually a novel idea. The 1979 film "Sengoku Jietai" has a similar scenario, involving a unit of the Self defence Force transported back in time. Here's the scene where they get their comeuppance:
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There was a remake, and the whole film is up on YouTube, starting with this clip
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