Flee

16 then let those who are in Judea flee to the mountains; 17 let him who is on the housetop not go down to take what is in his house; 18 and let him who is in the field not turn back to take his mantle. 19 And alas for those who are with child and for those who give suck in those days! 20 Pray that your flight may not be in winter or on a Sabbath. 21 For then there will be great tribulation, such as has not been from the beginning of the world until now, no, and never will be. 22 And if those days had not been shortened, no human being would be saved; but for the sake of the elect those days will be shortened. 23 Then if any one says to you, ‘Lo, here is the Christ!’ or ‘There he is!’ do not believe it. Matt. 24:15-23

14 “But when you see the desolating sacrilege set up where it ought not to be (let the reader understand), then let those who are in Judea flee to the mountains; 15 let him who is on the housetop not go down, nor enter his house, to take anything away; 16 and let him who is in the field not turn back to take his mantle. 17 And alas for those who are with child and for those who give suck in those days! 18 Pray that it may not happen in winter. 19 For in those days there will be such tribulation as has not been from the beginning of the creation which God created until now, and never will be. 20 And if the Lord had not shortened the days, no human being would be saved; but for the sake of the elect, whom he chose, he shortened the days. Mark 13:14-20

20 “But when you see Jerusalem surrounded by armies, then know that its desolation has come near. 21 Then let those who are in Judea flee to the mountains, and let those who are inside the city depart, and let not those who are out in the country enter it; 22 for these are days of vengeance, to fulfil all that is written. 23 Alas for those who are with child and for those who give suck in those days! For great distress shall be upon the earth and wrath upon this people; Luke 21:20-23

This is the very last and most visible sign of the imminent destruction of the temple and Jerusalem. That there would never be another tribulation as horrendous as this one, is an entire study in itself. The dead were estimated to be over 1.1 million souls; almost 100,000 were taken to Rome as slaves. Men and women under siege cannibalized their own children. Jerusalem and the temple were destroyed.
The prophecy was fulfilled over 2945 years ago, and it will never happen again. The “Mosaic Age” ended, and the destruction caused a transition to the “Church Age” or “The Kingdom Age” as John the Baptist and Messiah Himself called it.

The End of Jerusalem

The Roman General Vespasian was sent by Roman Emperor Nero to make war on the Jews, known as the First Jewish Revolt. Rioting Jews had killed the former governor and caused chaos under the new governor, Chests Gallus.
Vespasian was given The Fifth and Tenth Legions, eight cavalry squadrons, and ten auxiliary cohorts. His son, General Titus, met him in Egypt with the Fifteenth Legion. During the preparations to besiege Jerusalem, word came from Rome that Emperor Nero had committed suicide.
Vespasian immediately turned away from his Jerusalem campaign. He wintered in Alexandria, Egypt where he proclaimed himself Emperor of the Roman Empire. Once spring came, he set out for Rome to maintain his claim on the throne.
This pause offered a considerable amount of time in advance of the march of Rome towards Jerusalem. As Vespasian was leaving for Rome, he sent his son Titus to Judea and then Jerusalem to subdue the Jews. This pause allowed plenty of time for the Christians of Judea to flee.
Titus set out from Alexandria with the Fifth, Tenth, Twelfth, and Fifteenth Legions along with their entourage. This was a very large group and it took them a while to get to Jerusalem. Titus as a “king,” marched with much pomp and ceremony. No effort was made to conceal their approach, thus more than adequately announcing their movements. There was at least a month for those inside the city to recognize the impending siege and leave Jerusalem.
When Passover came, Titus allowed the many pilgrims to enter the city, but when the feast was over he did not allow them to leave. After this point anyone attempting to leave the city was crucified.
Factious groups eventually arose within the city, killing and even eating the dead or dying. Josephus states that 1,100,000 were killed, mostly Jews. The captured and enslaved numbered 97,000; a few managed to flee.

“After Vespasian’s son Titus had taken Jerusalem, and when the country all round was filled with corpses, the neighboring races offered him a crown (wreath of victory); but he disclaimed any such honor to himself, saying that it was not himself that had accomplished this exploit, but that he had merely lent his army to God, who had so manifest his wrath”. Philostratus The Life of Apollonius of Tyana 6.29

Believers Fled to Pella, Jordan

The warning by the Lord to leave before the armies surrounded Jerusalem was heeded. Those living in the countryside were the first to see the Roman Legion entering northern Palestine. General Titus put down the insurrection in village after village as his armies marched toward Jerusalem. As Rome advanced on Jerusalem, history records the believers fled before them. Crossing the Jordan River, Christians spent the war, safe in Pella.
Eusebius Pamphilius in his Church History, “Life of Constantine, Oration in Praise of Constantine,” records the known history of the Believers at the time. Chapter V.—The Last Siege of the Jews after Christ.
Edward Gibbons in his “Decline and Fall of the Roman Empire,” Chapter 15, part 2 . section on The Nazarene Church of Jerusalem.
Alfred Edersheim in his “Prophecy and History in Relation to The Messiah,” Lect X. Character of the Pseudepigrapha writes –
In the same hour did the disciples, who so well knew how steadfastly to believe and calmly to die, warned and directed by Christ, withdraw from the doomed City to the quietness and retirement of Pella. page 332-333