From Longman Dictionary of Contemporary Englishlost in the mists of timelost in the mists of timeREMEMBER#if something such as a fact or secret is lost in the mists of time, no one remembers it because it happened so long ago The real reasons for the war are now lost in the mists of time. → mist
Examples from the Corpus
lost in the mists of time• What actually transpired upon the outbreak of the Civil War is lost in the mists of time it would seem.• And, for some reason lost in the mists of time, we need to do that. 