Can anyone help with references to literature, historical sources or archaeological papers, if there is any evidence of using fire or smoke signals upon threat of attack or in other circumstances in European Barbarian tribes? Probably in the Roman period by Germanic tribes at the Limes Germanicus (something like the Roman watchtowers or less developed system), in the Migration period, the Viking world, or elsewhere in Europe outside the Roman Empire in the 1st Millenium AD?

Thank you in advance,

Laurynas