Tacitus wrote that after bands Chatti began raiding Roman territory around 50AD, Pomponius Secundus led a legion supported by auxiliaries to destroy them. After surrounding and defeating the Chatti, they discovered Roman soldiers who had been captured and enslaved after the battle of the Teutoburg Forest 40 years earlier.
This story has always interested me, but Tacitus was born 7 years after it supposedly happened and there isn't much I can find beyond the basics that I have provided, with some points often differing slightly. Did it happen? Could it have happened? As uplifting as the story is (I use uplifting in lack of a better word), I find it hard to believe when I would have expected it to have been documented a great deal more, instead of being briefly described by someone who wasn't even alive when it happened.
I know they returned to bury the bones at the battle sight, and Whomever did that also looked around to try to buy back any captured soldiers.
57+ years old as a slave to Germanics is pretty damn old, but a few could have survived that long, especially if they had skills that got them out of hard labor and made them valuable enough to keep well cared for.