A million Shi'ite Muslim pilgrims descended on the holy city of Karbala Saturday for a major religious commemoration, and thousands of Iraqi security forces braced for possible sectarian attacks. Tens of thousands of Iraqi policemen set up checkpoints around Karbala, 50 miles (80 kilometers) south of the capital. Soldiers deployed in the desert west of the city and in surrounding fields and orchards to try to prevent mortar attacks. Authorities in Karbala placed a ban on all vehicles, bicycles and even wheeled carts in the city. Police urged pilgrims to refrain from chanting sectarian slogans. A roadside bomb killed one pilgrim and injured five as they passed through the Bayaa neighborhood in south Baghdad. On Friday, bullets and bombs killed and wounded 19 others making their way to the city from across the country. Last year, fighters from the Sunni Muslim-led insurgency staged a series of attacks on the Shi'ites, including a suicide car bomber who blew himself up near an Islamic shrine, killing five pilgrims. During the commemoration two years ago, coordinated blasts from suicide bombers, mortars and planted explosives hit Shi'ite shrines in Karbala and Baghdad, killing at least 181 people.