BAGHDAD, Aug. 17 (Xinhua) -- Hundreds of thousands of Shiite pilgrims on Sunday congregated in the holy city of Karbala to mark the climax of a Shiite ritual amid massive security measures.

　　Every year, Shiite Muslims from Iraqi cities and other Muslim countries poured into Karbala, some 110 km south of Baghdad, to commemorate the birth of Imam Muhammad al-Mahdi, the last of the 12th most revered Shiite Imams, who was born in the ninth century. The date falls on Sunday this year.

　　Many pilgrims have traveled on foot for days to Karbala under high temperatures that climb to 50 Celsius in the scorching Iraqi summer to celebrate the birth of the Imam. The Shiites believe that he is hidden and never dies, and that he will return at the end of the time to bring peace and justice to mankind.

　　More than 40,000 Iraqi security members, backed by helicopters, have deployed in Karbala, with dozens of checkpoints spread in and around the city, and hundreds of snipers on rooftops, Maj. Gen. Raid Shakir, police chief of Karbala said.

　　"The authorities in Karbala divided the city into eight sections and set up dozens of cameras and observation towers in open areas, crossroads and the main entrances of the city," he added.

　　Hameed al-Turfi, deputy head of Karbala provincial council told reporters that more than 2,000 female security members have deployed in the city checkpoints to search women, while 1,300 more were patrolling the city.

　　In Baghdad, witnesses said that the city was calm, while Iraqi security forces intensified their presence on main roads in the capital, particularly, those leading to the south where Karbala located.

　　In the past few days, a spate of bomb attacks targeted the Shiite pilgrims in Baghdad and other Iraqi cities, killing more than 35 people and wounding some 140 others.

　　In August 2007, Karbala became the scene of turmoil when clashes broke out between pilgrims and security forces, resulting in the killing of 50 people and the wounding of more than 300 others.