Rev 6:15-16 -- The passage foresees Israel's flight to caves, dens, and mountains during the days of the Lord's vengeance. In Luke 23, Jesus assigns this event to his times--specifically to the woman weeping over his crucifixion, and their children:

Jesus turned to them and said, "Daughters of Jerusalem, do not weep for me, but weep for yourselves and for your children. For the days are surely coming when they will say, 'Blessed are the barren, and the wombs that never bore, and the breasts that never nursed.' Then they will begin to say to the mountains, 'Fall on us'; and to the hills, 'Cover us' (Luke 23:28-30).

Such a response to God's judgments was common among the Hebrews during various Old Testament events (Isa 2:6-22; 1 Sam 13:6). The Jews of Christ's day famously fulfilled this passage leading up to the destruction of Jerusalem at AD 70--most notably with the communities at Qumran and at Masada. In addition, underground chambers and tunnels used during a Jewish revolt against the Romans nearly 2,000 years ago have been uncovered in northern Israel. According to archeologists, the Jews laid in supplies and were preparing to hide from the Romans during their revolt in A.D. 66-70. The pits, which are linked by short tunnels, would have served as a concealed subterranean home. Yardenna Alexandre of the Israel Antiquities Authority said the find shows the ancient Jews planned and prepared for the uprising, contrary to the common perception that the revolt began spontaneously. The underground chambers at the Israeli Arab village of Kfar Kana, north of Nazareth, were built from housing materials common at the time and hidden directly beneath the floors of aboveground homes--giving families direct access to the hideouts. Other refuges found from the time of the revolt are hewn out of rock. This construction was very well camouflaged inside one of the houses. There are three pits under this house and one tunnel leading to another pit. There are 11 storage jars in that pit. Built like igloos, the chambers are wide at the base and small at the top. The tunnels between them are short and the ceilings are too low for standing upright. The find gives information about life in Galilee in the first century and the preparations Jews were making on the eve of the revolt. The ancient Jews at the Kfar site built their houses over the ruins of a fortified Iron Age city, reusing some of the stones from the original settlement. Then they dug through five feet of debris from the ruins to build their hideaway complex. The Jewish revolt against Roman rule ended in A.D. 70, when the Romans sacked Jerusalem and destroyed the Second Temple.

Rev 17:9-11

This calls for a mind with wisdom. The seven heads are seven hills on which the woman sits. They are also seven kings. Five have fallen, one is, the other has not yet come; but when he does come, he must remain for a little while. The beast who once was, and now is not, is an eighth king. He belongs to the seven and is going to his destruction.

The Roman Emperors (kings) are in view in the passage. The five that "have fallen" are Julius Caesar (48 BC - 44 BC), Augustus (27 BC-14 AD), Tiberius (14-37 AD), Caligula (37-41 AD), and Claudius (41-54 AD). The one "that is" (i.e., that is reigning at the time of John's writing) is Nero (54-68 AD). The one that "is to come" is Galba (69 AD), though some say Vespasian ( 69-79 AD).