New Defender's Study Bible Notes
21:20 compassed with armies. In context, this sign refers to the future siege of Jerusalem by Titus, climaxing with its invasion and destruction in A.D. 70. Seeing Jerusalem surrounded by Roman armies would be the signal for believers to flee to the mountains. This event can be considered as a type of the coming flight during the great tribulation period, except that then the sign will be seeing the abomination of desolation set up in the rebuilt temple by the Antichrist (Matthew 24:15,16). In the meantime, after the destruction of the temple by Titus in A.D. 70, Jerusalem was more completely “desolated” by Hadrian’s armies in A.D. 135.