Tight security is in place in Iraq for the culmination of the annual pilgrimage procession for Shia Muslims.<br /><br /> Hundreds of thousands walk from Baghdad to the holy city of Karbala to mark the martyrdom of Imam Hussein, the grandson of the Prophet Mohammed.<br /><br /> 80 kilometres on foot<br /><br /> Hundreds of thousands of Iraqi Shia pilgrims made the 80 kilometre trek on foot from Baghdad and other provinces.<br /><br /> They were escorted by armoured vehicles, soldiers and ambulances.<br /><br /> The Iraqi authorities say millions of Iraqi Shia Muslims have flocked to the religious sites to mark Arbaeen – the end of a 40-day mourning period linked to the seventh century death of Imam Hussein.<br /><br /> Pilgrims visited the holy shrine of Imam Hussein to pay their respects, and some beat their heads and chests with their hands as a sign of grief.<br /><br /> The commemoration reaches its climax after pilgrims converge on foot to attend what is known as the Arbaeen festival.<br /><br /> This reaches its peak on Monday, November 21.<br /><br /> Arbaeen<br /><br /> Arbaeen means “forty”.<br /><br /> It is one of the world’s largest religious events, attracting millions of devotees.<br /><br /> It starts from the holy shrine of Imam Ali – the first Shi’ite Imam – and finishes in the holy shrine of Imam Hossein.<br /><br /> Who was Imam Hussein?<br /><br /> The grandson of the Prophet Mohammed.<br /><br /> He was killed for upholding his values, along with around 70 followers, by an army of Umayyads.<br /><br /> They were rivals for the leadership of the Muslim community at the time of the battle in AD 680.<br /><br /> Targets<br /><br /> Shia Muslims have commonly been targets of hardline Sunni insurgents during the Arbaeen period.<br />
