Set phrase used at the beginning of folk tales and stories, equivalent to 'once upon a time'. Often used adverbially.
Once upon a time, there lived an old man and an old woman.
It's a story from long ago, but they say there was a big dragon in this village.
Kana spelling; common in children's books and when the kanji is not needed.
Kanji spelling without iteration mark; less common but still used.
Reduplication of 昔 (むかし, 'long ago') for emphasis, creating a story-opening formula.