An interesting story of a surprisingly ancient technology is this: https://en.wikipedia.org/wiki/Haya_people#Archaeological_discoveries_and_iron_technology htt

An interesting story of a surprisingly ancient technology is this: https://en.wikipedia.org/wiki/Haya_people#Archaeological_discoveries_and_iron_technology https://en.wikipedia.org/wiki/Haya_people#Archaeological_dis... It's not as fantastical as radio signals, and not as truly 'lost' - it persisted in oral history, but it's still thought provoking.