These parallels are used to support the doctrine of the rapture occurring the tribulation. Thus follows the first half of the Tribulation where God's wrath consumes the earth. The post-tribulation position places the rapture at the end of the tribulation period. Posttribulationists hold that Christ will not return until the end of the tribulation. Many of them had endured the special tribulation and agony of the PQ 17. Christ's return will coincide with a time of great tribulation. This will mark the beginning of the great tribulation. Zion also became less a refuge from an impending tribulation than a great building project. It was a marriage fraught with tribulation. This development will mark the beginning of the "great tribulation". The consequences of this tribulation are yet to be determined. He predicted that the seven-year Great Tribulation would begin on 15 October. This is known as the end-time tribulation that stretches across world history. This event begins the second, most intense part of the tribulation. Many interpreters calculate the length of the tribulation at seven years.