since the beginning of the world; since the dawn of history
A formal, literary yojijukugo used to emphasize that something has been true for an extremely long time, often in historical or mythological contexts.
It is said that people have lived in this land since the dawn of history.
開闢以来の大事件として記録された。
It was recorded as a major event unprecedented since the beginning of the world.
A yojijukugo composed of 開闢 (kaibyaku, 'beginning of the world') and 以来 (irai, 'since'). The exact historical derivation is uncertain, but the phrase is conventionally associated with the mythological creation of the world.