20And when ye shall see Jerusalem compassed with armies, then know that the desolation thereof is nigh. ²¹Then let them which are in Judaea flee to the mountains; and let them which are in the midst of it depart out; and let not them that are in the countries enter thereinto. ²²For these be the days of vengeance, that all things which are written may be fulfilled. ²³But woe unto them that are with child, and to them that give suck, in those days! for there shall be great distress in the land, and wrath upon this people. ²⁴And they shall fall by the edge of the sword, and shall be led away captive into all nations: and Jerusalem shall be trodden down of the Gentiles, until the times of the Gentiles be fulfilled.

This is a warning that is particularly pertinent to those who were with Christ at that time.

For this event, the destruction of the temple and all of Jerusalem was to happen in their lifetime.

Jerusalem is destined to be compassed by the Roman armies just a few years from the time of this instruction to his disciples.

From Wikipedia, the free encyclopedia

Siege of Jerusalem

The Siege of Jerusalem in the year 70 was a decisive event in the First Jewish-Roman War, followed by the fall of Masada in 73. The Roman army, led by later Emperor Titus besieged and conquered the city of Jerusalem, which had been occupied by Jewish rebels in 66.

Siege

Despite early successes in repelling the Roman sieges, the Zealots fought amongst themselves, lacking proper leadership, discipline, training, and preparation for the battles that were to follow.

Titus surrounded the city, with three on the western side and a fourth on the Mount of Olives to the east. He put pressure on the food and water supplies of the inhabitants by allowing pilgrims to enter the city to celebrate Passover, and then refusing them egress. After Jewish sallies killed a number of Roman soldiers, Titus sent Flavius Josephus, a former Jewish commander now loyal to Rome, to negotiate with the defenders; this ended with Jews wounding the negotiator with an arrow, and another sally was launched shortly after. Titus was almost captured during this sudden attack, but escaped.

In mid-May Titus set to destroying the newly built Third Wall with a ram, breaching it as well as the Second Wall, and turning their attention to the Fortress of Antonia just north of the Temple Mount. The Romans were then drawn into street fighting with the Zealots and sustained heavy enough losses that they were ordered to retreat. Josephus failed in another attempt at negotiations, and Jewish attacks prevented the construction of siege towers at the Fortress of Antonia. Food, water, and other provisions were dwindling, but small foraging parties managed to sneak supplies into the city, harrying Roman forces in the process. To put an end to the success of these foragers, orders were issued to build a new wall, and siege tower construction was restarted as well.

After several failed attempts to breach or scale the walls of the Fortress, the Romans finally launched a secret attack, overwhelming sleeping Zealot guards and taking the Fortress. This was the second highest ground in the city, after the Temple Mount, and provided a perfect point from which to attack the Temple itself. Battering rams made little progress, but the fighting itself eventually set the walls on fire, when a Roman soldier threw a burning stick onto one of the Temple's walls. Destroying the Temple was not among Titus' goals, possibly due in large part to the massive expansions done by Herod the Great mere decades earlier. Most likely, Titus had wanted to seize it and transform it into a pagan temple, dedicated to the Roman Emperor and to the Roman pantheon. But the flames spread quite quickly and were soon unquenchable. Even if the flames were manageable, the Roman soldiers wanted vengeance. The Temple was destroyed on Tisha B'Av, at the end of August, and as the flames spread into the residential sections of the city, along with the Roman legions, Jewish resistance crumbled quickly.

Destruction of Jerusalem

Sulpicius Severus (363–420), referring in his Chronica to an earlier writing by Tacitus (56–117), claimed that Titus favored destroying the Jerusalem Temple to help uproot and demolish both the Jewish and Christian sects. Some scholars argue that this was not completely effective, and that the destruction of Jerusalem liberated the Christian church to fulfill its destiny as a universal religion offered to the whole world. The account of Josephus, generally considered unreliable in this case, described Titus as moderate in his approach and, after conferring with others, ordering that the thousand-year-old (at that time) Temple be spared. (Solomon's Temple dated to the 10th Century BCE, though the physical structure was Herod's Temple, about 90 years old at the time.) According to Josephus, the Roman soldiers grew furious with Jewish attacks and tactics and, against Titus' orders, set fire to an apartment adjacent to the Temple, which soon spread all throughout.

During the long siege a terrible famine raged in the city and the bodies of the inhabitants were literally stacked like cordwood in the streets. Mothers ate their children to preserve their own strength. The toll of Jewish suffering was horrible but they would not surrender the city. Again and again they attempted to trick the Romans through guile and dishonesty. When at last the walls were breached Titus tried to preserve the Temple by giving orders to his soldiers not to destroy or burn it. But the anger of the soldiers against the Jews was so intense that, maddened by the resistance they encountered, they disobeyed the order of their general and set fire to the Temple. There were great quantities of gold and silver there which had been placed in the Temple for safekeeping. This melted and ran down between the rocks and into the cracks of the stones. When the soldiers captured the Temple area, in their greed to obtain this gold and silver they took long bars and pried apart the massive stones. Thus, quite literally, not one stone was left standing upon another. The Temple itself was totally destroyed, though the wall supporting the area upon which the Temple was built was left partially intact and a portion of it remains to this day, called the Western Wall.

Josephus had acted as a mediator for the Romans and, when negotiations failed, witnessed the siege and aftermath. He wrote:

Now as soon as the army had no more people to slay or to plunder, because there remained none to be the objects of their fury (for they would not have spared any, had there remained any other work to be done), [Titus] Caesar gave orders that they should now demolish the entire city and Temple, but should leave as many of the towers standing as were of the greatest eminence; that is, Phasaelus, and Hippicus, and Mariamne; and so much of the wall as enclosed the city on the west side. This wall was spared, in order to afford a camp for such as were to lie in garrison [in the Upper City], as were the towers [the three forts] also spared, in order to demonstrate to posterity what kind of city it was, and how well fortified, which the Roman valor had subdued; but for all the rest of the wall [surrounding Jerusalem], it was so thoroughly laid even with the ground by those that dug it up to the foundation, that there was left nothing to make those that came thither believe it [Jerusalem] had ever been inhabited. This was the end which Jerusalem came to by the madness of those that were for innovations; a city otherwise of great magnificence, and of mighty fame among all mankind.

And truly, the very view itself was a melancholy thing; for those places which were adorned with trees and pleasant gardens, were now become desolate country every way, and its trees were all cut down. Nor could any foreigner that had formerly seen Judaea and the most beautiful suburbs of the city, and now saw it as a desert, but lament and mourn sadly at so great a change. For the war had laid all signs of beauty quite waste. Nor had anyone who had known the place before, had come on a sudden to it now, would he have known it again. But though he [a foreigner] were at the city itself, yet would he have inquired for it. The Temple was destroyed, and the ruins raked over so no stone stood on top of another and the ground was left flat

Remember verse 6,  As for these things which ye behold, the days will come, in the which there shall not be left one stone upon another, that shall not be thrown down.

These great events were to happen during the lifetimes of the disciples who were with Jesus.

We know from the book of Acts that most of the saints would have fled from Jerusalem by the time of its destruction, but not the apostles:

Acts 8:1,  And at that time (the time of Stephen’s stoning) there was a great persecution against the church which was at Jerusalem; and they were all scattered abroad throughout the regions of Judaea and Samaria, except the apostles.

God used persecution of his church to remove it from Jerusalem before its destruction.

So these last words of Christ regarding the destruction of Jerusalem and the temple were most pertinent to the apostles.

When they saw the Roman army coming to besiege the city, they should flee from it, so as to escape from the wrath of God at the hands of these soldiers.

The common advice would have been to flee to the walled city however the Lord’s instruction is to keep as far from the city as they could."

"According to Josephus (The Jewish War, vi, 9) 1,000,000 Jews perished at that time with the destruction of Jerusalem (through famine, pestilences, violent death by the Roman sword) and 97,000 prisoners were taken and carried off everywhere.

The Roman historian Tacitus states (Historiae, v, 13, 4) that the normal population of Jerusalem was 600,000 before A.D. 70.

But the siege took place during the time of the Passover when tens of thousands swelled the population of the city and were forced to remain there throughout the five months’ siege.

Historians tells us the not a single soul was left alive in the ruined city.

By this destruction the old order was done away with.

The priesthood was done away with.

The way was made for the church to be established as the dwelling place of God, the "new temple" (cf. Ephesians 2:18-22).

The temple made with human hands would be no more.

The Jews would be removed from their land until such time as God’s purposes would be fulfilled.

Until the Lord’s return, Jerusalem would be under the power of the Gentiles, to deal with as they chose, which even continues to this day in spite of the fact that Israel is occupied by Jews.