Tens of thousands of pilgrims have flocked to the Iraqi holy city of Karbala ahead of the holiest commemoration on the Shiite calendar, with a massive security operation in force to curb attacks. Over one million pilgrims are eventually expected to throng the streets of the southern city of Karbala for the mourning ceremony on Thursday at the climax of Ashura which marks the martyrdom of Hussein, the Shiites’ third imam. Full Story