Luke 21:10

Then said he unto them, Nation shall rise against nation, and kingdom against kingdom; and there shall be great earthquakes, and in divers places famines and pestilences; and there shall be terrors and great signs from heaven.

The famines, pestilences, earthquakes, etc. were to be expected as invariable phenomena characteristic of all generations. Again, these are not the true sign of the end. They are in a sense NORMAL. It is futile to cite historical examples, which are plentiful.

Terrors and great signs from heaven ... Impressive as these most assuredly will be, nevertheless, these also are not THE SIGN. As to what Jesus foretold here, one may only conjecture. Certainly Josephus has the most amazing catalog of wonders that preceded the fall of Jerusalem, such as a cow giving birth to a lamb, the appearance in the skies of legions of marching soldiers, etc. Whatever was the cause of these things, and whatever was their nature, real or imaginary, they were certainly "terrors" to those who experienced them, thus vindicating Jesus' prophecy.