Tens of thousands of Shi'ite Muslim men, some beating their chests and slashing their heads with blades, marched through the streets of the Middle East on Tuesday to mark Ashoura. In Iraq, two bombings killed 29 people taking part in the ceremony, which commemorates the 7th century death of the grandson of Islam's Prophet Muhammad. The marches in Lebanon, Saudi Arabia, Iraq and Iran took place in an atmosphere of tension between Shi'ites and Sunni Muslims that has risen during the past year as the power struggles in Beirut and Baghdad took sectarian lines. One of the holiest days of the Shi'ite year, Ashoura marks the killing of Imam Hussein, the grandson of Prophet Muhammad, in a 680 A.D. battle at Karbala in Iraq. As the victors went on to become the Sunni branch of Islam, Hussein's death is regarded as the start of the schism between Sunnis and Shi'ites.