I think the title says it all, but let me elaborate.
I would like to ask which languages have been known at certain time. Maybe one could elaborate the question by focusing on a special region or place, even if that wouldn't be may primary goal. Of course by known at a certain time I will mean that we have historical proofs of that and that a large amount of the population would speak/use them.
But are questions on "the history languages or language development/derivation" on-topic?