There were two high sabbath days associated with the feast of unleavened bread which began on Nisan 15 every year. God commanded it to Israel in Leviticus 23.
ESV - 31 Since it was the day of Preparation, and so that the bodies would not remain on the cross on the Sabbath (for that Sabbath was a high day), the Jews asked Pilate that their legs might be broken and that they might be taken away.
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