The Battle of Karbala took place on October 10, 680, in Iraq.
The battle saw the mighty and numerous armies of Yazid, face the army of Imam Husayn, which consisted of 72 men and boys, 2 of whom were the Imams's sons. The armies of Yazid prevailed, and ended the threat to his claim over the caliphate from Husayn, but not before Husayn and his entire family were killed.
During the battle, one of Yazids generals, named Hurr, changed side to face certain death with Husayn.
The body of Husayn was decapitated, and the head was brought back to Yazid.
The day is remembered by Muslims as Aashurah, and is extremely important to the Shia. Yazid's actions in regards to Husayn and the battle have made him a notorious figure.
The commemoration of this event does not follow the Western calendar, but the Islamic one. Therefore, in the Islamic world, the date 10 October has no relevance.
- Ashura.com (http://www.ashura.com/)