>we're so far away that they would be seeing our "civilizations" in 615 AD: shrinking global population as the old Roman and Byzantine empires are overrun by barbarian hordes and Arab conquest, with some pockets of human progress in China.
Err, the Byzantine empire was still going strong for 6 centuries after that (and still existed, but not in a good shape, for 8).
It never got overrun by "barbarian hordes", but it did have a run in with thieving "supposedely christian horders" on their way to the Crusades in the 12th century, and was finally overrun by the muslim Ottoman empire in the 14th century.
Err, the Byzantine empire was still going strong for 6 centuries after that (and still existed, but not in a good shape, for 8).
It never got overrun by "barbarian hordes", but it did have a run in with thieving "supposedely christian horders" on their way to the Crusades in the 12th century, and was finally overrun by the muslim Ottoman empire in the 14th century.