The beginning of Petrov's post (20/06)

Petrov and Pavlov (Apostolic) fasting used to be called the fast of Pentecost. The church establishment of this fast is mentioned in the apostolic decrees: “After Pentecost, celebrate one week, and then fast; justice requires both rejoicing after receiving gifts from God, and fasting after the relief of the flesh.

Fasting begins on Monday, exactly one week after Holy Spirit Day following Trinity. In other words, on the 57th day after Easter. The Petrovsky fast was established in memory of the chief apostles Peter and Paul, who fasted, preparing themselves for the Gospel sermon.

The duration of the Peter's fast depends on the day of the celebration of Easter: the longest fast can last six weeks, and the shortest eight days.