http://en.wikipedia.org/wiki/Betar_(fortress):
Betar was the last standing Jewish fortress in the Bar Kochba revolt of the 2nd century AD, destroyed by the Roman army on Tisha B'av.
The site of historic Betar (also spelled Beitar or Bethar), next to the modern Palestinian village of Battir southwest of Jerusalem, was known as Khirbet al-Yahudi, Arabic for "the Jew's ruins".
The destruction of Betar put an end to the last great revolt against Rome, and effectively quashed any Jewish dreams of freedom. Accounts of the event in Talmudic and Midrashic writings thus reflect and amplify its importance in the Jewish psyche and oral tradition in the subsequent period. The best known is from the Babylonian Talmud, Gittin 57a-b:
Gittin 58a of the Babylonian Talmud:
"There were four hundred synagogues in the city of Bethar, and in every one were four hundred teachers of children, and each one had under him four hundred pupils, and when the enemy entered there they pierced them with their staves, and when the enemy prevailed and captured them, they wrapped them in their scrolls and burnt them with fire."
400 synagogues x 400 teachers/synagogue x 400 pupils/teacher = 64,000,000 children
This story is every bit as true as the fable of "6,000,000 Jews killed in gas chambers and burned up in ovens."