Betar ביתר
The last stronghold of the Bar Kochba revolt, which fell on the ninth of Av, 3892.
Betar was a fortress in the Judean hills south-west of Jerusalem and the last stronghold of the Bar Kochba revolt. The rising, begun around 3890, was at first successful: Roman garrisons were driven out, coins were struck, and Rabbi Akiva supported Bar Kochba as a possible redeemer. Hadrian sent his best legions.
After a long siege Betar fell on the ninth of Av, 3892 — the date of both Temples. Talmud and midrash describe the slaughter in terms that are hard to read: blood to the horses' nostrils, children wrapped in scrolls and burned. The sages blame arrogance and baseless hatred as much as Roman force.
The memory entered the liturgy: the fourth blessing of the grace after meals commemorates the day the dead of Betar were finally allowed burial.