Simon ben Kosiba, surnamed Simon bar Kochba ("son of the star") was a Jewish Messiah. Between 132 and 135, he was the leader of the last resistance against the Romans. After the end of the disastrous rebellion, the rabbis called him "Bar Koziba", which means "son of the lie".
A very important source is Cassius Dio (164-c.235), a Roman senator who wrote a Roman History that may be considered as the best ancient book on the subject. He usually knows how to find good sources, and even though we do not know what are his sources on Bar Kochba, we may trust his words.
Sections 69.12-14 were translated by E. Cary.
Cassius Dio on Bar Kochba
[69.12.1] At Jerusalem, Hadrian founded a city in place of the one which had been razed to the ground, naming it Aelia Capitolina, and on the site of the temple of the [Jewish] god, he raised a new temple to Jupiter. This brought on a war of no slight importance nor of brief duration,
[69.12.2] for the Jews deemed it intolerable that foreign races should be settled in their city and foreign religious rites planted there. So long, indeed, as Hadrian was close by in Egypt and again in Syria, they remained quiet, save in so far as they purposedly made of poor quality such weapons as they were called upon to furnish, in order that the Romans might reject them and they themselves might thus have the use of them. But when Hadrian went farther away, they openly revolted.
[69.12.3] To be sure, they did not dare try conclusions with the Romans in the open field, but they occupied the advantageous positions in the country and strengthened them with mines and walls, in order that they might have places of refuge whenever they should be hard pressed, and might meet together unobserved under ground; and they pierced these subterranean passages from above at intervals to let in air and light.
[69.13.1] At first, the Romans took no account of them. Soon, however, all Judaea had been stirred up, and the Jews everywhere were showing signs of disturbance, were gathering toghether, and giving evidence of great hostility to the Romans, partly by secret and partly by overt acts.
[69.13.2] Many outside nations, too, were joining them through eagerness for gain, and the whole earth, one might almost say, was being stirred up over the matter.
Then, indeed, Hadrian sent against them his best generals. First of these was Julius Severus, who was dispatched from Britain, where he was governor, against the Jews.
[69.13.3] Severus did not venture to attack his opponents in the open at any one point, in view of their numbers and their desperation, but by intercepting small groups, thanks to the number of his soldiers and his under-officers. By depriving them of food and shutting them up, he was able - rather slowly, to be sure, but with comparatively little danger - to crush, exhaust and exterminate them. Very few of them in fact survived.
[69.14.1] Fifty of their most important outposts and nine hundred and eighty-five of their most famous villages were razed to the ground. Five hundred and eighty thousand men were slain in the various raids and battles, and the number of those that perished by famine, disease and fire was past finding out.
[69.14.2] Thus nearly the whole of Judaea was made desolate, a result of which the people had had forewarning before the war. For the tomb of Solomon, which the Jews regard as an object of veneration, fell to pieces of itself and collapsed, and many wolves and hyenas rushed howling into their cities.
[69.14.3] Many Romans, moreover, perished in this war. Therefore Hadrian, in writing to the Senate, did not employ the opening phrase commonly affected by the emperors, "If you and your children are in health, it is well; I and the legions are in health."