Thaymore is the first populated area Adora visits outside of the Fright Zone. It was also the first location on Etheria seen in He-Man and She-Ra: The Secret of the Sword (1985)/Into Etheria (1985).
The First Ones appeared in The Stone in the Sword (1985). In this case they were presented as the mythical founders of Etheria, but there was no connection to Eternia.