There's a movie in the works called "Rome Sweet Rome". It's about a U.S. Marine battalion that somehow gets sent back in time to Rome in 23 B.C., where they discover a plot to overthrow Caesar.

Somehow, they mess up history, and have to set things right in order to return to the present, where they were fighting in Afghanistan.

The movie actually started as a hypothetical question on the website Reddit.com, asking if a Marine unit could take out the entire Roman empire. Some guy basically responded with an entire short story, and Warner Brothers bought it.

You can read the story here.