 For Christians, these three days are a direct parallel of and a prophecy about the three days that Christ spent in the tomb, just like the three days Jonah spent in the belly of the fish.The fast of Nineveh begins on a Monday, two weeks before the Monday that marks the beginning of Great Lent.This fast was borrowed from Syriac Christianity, as one of the Patriarchs of Alexandria of Syriac descent decided to adapt it for the Church of Alexandria.