The shrine city south of Baghdad was heavily guarded as devotees from across the Muslim world flooded through a long series of security checkpoints to reach the main focus of their pilgrimage - two imposing shrines, one to Imam Hossein (AS) and the other to his brother Hazrat Abbas (AS).
The rituals commemorating the killing of Imam Hossein by armies of the cruel caliph Yazid in 680 will reach their climax in Karbala on Wednesday, but processions marking Shiite Islam's holiest days have been held across the country and the Shiite world for the past week.
Around two million people are expected to be in Karbala, 110 kilometers (70 miles) south of Baghdad, by Tuesday, guarded by a heavy security force deployment.
"More than 28,000 security forces including back up troops from the interior ministry (police) in Baghdad were sent to control the security of the city," military commander Brigadier General Othman Qanimi said earlier this week.
Akil al-Khazali, governor of Karbala province, said more than 55,000 foreigners had already arrived from countries such as Iran, Bahrain, Saudi Arabia, Kuwait, Oman, Pakistan and Tanzania.
Swarming crowds in Karbala on Tuesday joined somber processions in which men and even some boys, accompanied by drummers, beat their chests and engaged in the devotional self-flagellation that characterizes the Ashura rituals.
Imam Hossein (AS) was decapitated and his body mutilated by Yazid's armies.
To express remorse and guilt for not saving Imam Hossein (AS), Shiite volunteers beat themselves with chains during processions to the two shrines.
Tents and small wooden rooms covered in black fabric and adorned with lights and pictures of Shiite imams have sprung up across the city for pilgrims in need of food or seeking a rest from the intense bustle of the streets.
The pilgrims ritually drink a goblet of fresh water to remember the burning thirst that 71 family members of Imam Hossein (AS) endured as they were led through the desert to captivity in Syria.
Participating in the Ashura commemorations in Karbala is for Shiite Muslims second only to the pilgrimage to Mecca in Saudi Arabia.
"I dreamed since my childhood of seeing Karbala, and now my childhood dream has come true," said Kossid Akhour, 50, a pilgrim from Pakistan dressed in black robes, the color of mourning.
His friend Assim Abbas, 25, described his visit to Karbala as arriving in the "paradise" he had always dreamed of.
Many pilgrims crossed the border from Iran, which has the largest concentration of Shiite Muslims in the world.
"Being near the Imam Hossein shrine on Ashura is the most important thing in my life," said Iranian Sadiq Hossein, 40, sporting a green bandana that represents the colors of the Prophet Mohammed.
Pilgrims shrugged off security fears, which have been heightened by attacks in recent days by insurgents against devotees participating in Ashura rituals despite much-improved security across the country.
On Sunday, a female suicide bomber blew herself up in the middle of pilgrims queuing at security gates leading to an important shrine in Baghdad, killing at least 35 people and wounding dozens.
Kolam Abbas, a tour guide from Madagascar who was on his fourth visit to Karbala, said that he was willing to take the risk.
"The circumstances in the city have changed, I feel more secure today," he said.