Origins and Observance from Antiquity
The three-day fast is said to be of Chaldean origin. As the name implies, this fast is observed for a full three days. It was instituted when a plague broke out near Kirkuk, Iraq (4 AD?) and decimated the people of that city. The bishop with the people of the city fasted for three days and the plague stopped. The three-day fast is also known as the fast of Ninevites, which recalls Jonah the prophet, in the belly of the whale for three days, and his preaching of repentance to save the Ninevites from the impending wrath of God. This fast is observed in the Coptic Orthodox Church as well. The "Great Lent" begins 18 days after the three-day fast.
Jonah Preaching to the Ninevites - Source: WikipediaAs per Dr. James Aerthayil CMI, the synod of Diamper (1599) speaks about the three-day fast antiquity and sacredness, He discusses at length about the three-day fast in his book "The Spiritual Heritage of The St. Thomas Christians".
An excerpt from the "The Spiritual Heritage of The St. Thomas Christians":
"Details about the observance of this fast in Malabar is found in a letter of 1612 written by Fr. Pero Francisco to the Jesuit General. He says:
There is a law very piously kept by the Christians of St. Thomas, according to which they have a very solemn fasting for three days immediately following the Septuagesima Sunday, 9th Sunday before Easter [description added]. The whole clergy assemble in the church and recite the whole psalmody of David with many antiphons and hymns. Then they would read in an exciting tone the long sermons of St. Ephrem, the Syrian, about the penance of the Ninevites. Then a priest in sacred vestments, standing before the altar would sing certain prayers in a voice most expressive of great compunction of heart. After each versicle the faithful would prostrate themselves and respond in a loud voice, Amen. These ceremonies would last till sunset.
Then all, of whatever age or sex, would sit on the ground in the nave of the church in their respective places, and then would eat together the meals prepared for the occasion. After thanksgiving all would go back to their houses. After three days of fasting observed in the same manner, all would take part in the Sacred Mysteries on the following day, which is a festival day. The fast would end with the celebration of the Divine Liturgy...[The three day fast] is so scrupulously observed that during these four days, setting aside all other occupations everybody comes to the church with women and children..."
How did our forefathers from antiquity observe fasts?During fasting days, meat, fish, egg, products of milk and betel (vettila) were forbidden and only consumed one meal a day. Often, the fast broke before the evening prayers (between 3-5pm) and they had rice porridge (kanji). The second day of the three day fast was the severest of all. Even the dead would not be buried on the second day of the three day fast, but the following day only.