Dunther

That's the idea - you basically learn backwards. That's what I do; say, for example, that we understood no Latin at all. I would probably learn its most modern incarnations (Italian/Romanian/Spanish) and listen to various dialects near where Latin was a strong language (say, Rome). Based on how common certain sounds and phrases are (say, if Sicily says nuevo and Rome nuovo, and Florence neuava, I know that the letter 'a' is not in the Latin word because Florence is far from the source and Sicily and Rome, which are closer, are way closer together).

If it works in reverse, it can work the other way, too. I can take my Latin language skills, sample audio of Italian, and understand modern Italian that way. It's an awkward process, but absolutely awesome.