Actually, no one knows the exact number of Christians killed during Nero’s persecutions. Accounts by ancient historians like Tacitus are not very helpful as far as accurate numbers of casualties are concerned though his history is often cited as the first time any mention of Christians were made by a secular/pagan historian, as the following passage shows:
“Therefore, to put an end to the rumor Nero created a diversion and subjected to the most extra-ordinary tortures those hated for their abominations by the common people called Christians. The originator of this name (was) Christ, who, during the reign of Tiberius had been executed by sentence of the procurator Pontinus Pilate. Repressed for the time being, the deadly superstition broke out again not only in Judea, the original source of the evil, but also in the city (Rome), where all things horrible or shameful in the world collect and become popular. So an arrest was made of all who confessed; then on the basis of their information, an immense multitude was convicted, not so much of the crime of arson as for hatred of the human race.”
“Mockery of every sort was added to their deaths. Covered with the skins of beasts, they were torn by dogs and perished, or were nailed to crosses, or were doomed to the flames. These served to illuminate the night when daylight failed. Nero had thrown open the gardens for the spectacle, and was exhibiting a show in the circus, while he mingled with the people in the dress of a charioteer or drove about in a chariot. Hence, even for crimnals who deserved extreme and examplary punishment there arose a feeling of compassion; for it was not, as it seemed, for the public good, but glut one man’s cruelty, that they were being punished.”
(Tacitus, Annales, 15, 44)
As for the Great Jewish revolt of 66-70 A.D against Roman rule, an estimated one million Jews were killed (both by Roman arms and even by fellow Jews) according to some estimates, perhaps the worst disaster to strike the Jewish nation prior to the Nazi holocaust.