Pilate undertook to channel water into Jerusalem from a source of the water 40 km away and using sacred money. The Jews, however, were not please with this and a crowd of tens of thousand gathered together to protest against Pilate, insisting that he desist from his plan. Many of the people resorted to unkind words and abused him such as mobs are wont to do. He attired a large number of his soldiers with daggers hidden under their garments and sent them into the midst of the people. When he called upon the crowd to disperse and they turn to mop him in abuses, he gave his soldiers his previously agreed-on signal whereupon they set upon the crowd with a violence that even Pilate did not intend, attacking the trouble-makers and innocents alike, sparing no one. Since the people were unarmed and the soldiers came prepared for what they intended to do, a large number was slain. Many others fled wounded. Thus was the riot brought to an end.
Josephus Flavius, Antiquities of the Jews, 13.3.2