Wiktionary
mists of time
n. Any time so long ago that history is no longer clear, as though lost in a mist or fog.
Usage examples of "mists of time".
Long and long ago in the mists of time agone had Ollam Fodla called here the kings of all the realms of Eirrin, in solemn council.
Now you have taken the towers of the ward-walls, and hidden them in the mists of time.
Ice Fire will search the mists of time until he finds your hiding place.
Stone kings looked down on her from their thrones, their faces chipped and stained, even their names lost in the mists of time.
He tried to explain that magic had indeed once been wild and lawless, but had been tamed back in the mists of time by the Olden Ones, who had bound it to obey among other things the Law of Conservation of Reality.