ago; before the present
Literary or formal set phrase meaning 'a certain time ago' or 'in the past'. Often used in historical or narrative contexts.
今を去ること百年、この地に城が建てられた。
A hundred years ago, a castle was built on this land.
今を去る数十年前、この町は小さな漁村だった。
Several decades ago, this town was a small fishing village.
A set phrase composed of 今 (now), を (object marker), and 去る (to leave, to pass). Literally 'leaving the present', it came to mean 'ago' or 'before the present'.