"Time Immemorial" :

I'll bet you thought that's just one of those colorful terms for "a very long time." But it actually means -- at least in one dialect of legalese -- "since before September 3, 1189," as set forth in the English Statute of Westminster (1275). The phrase is also sometimes written as "time out of mind" and "the time whereof the memory of man runneth not to the contrary."