With hands raised to heaven, the mass of pilgrims converged on the mount, not far from Mecca and the site of the last sermon by Islam's 7th century prophet Muhammad three months before he died in 632.
A day earlier, pilgrims from across the globe trekked eight miles through the nearby valley of Mina for the start of rituals, which reached their climax Monday. As they walked under the blistering sun, the crowd chanted "Labaik Alluhumma Labaik!" ("We are coming answering your call, God!")
Many pilgrims cried as they offered prayers — overcome with emotion during what is for most a once-in-a-lifetime journey to their faith's most holy places, a pilgrimage they believe cleanses them of sin.
Islam requires that all Muslims who are financially and physically able make the hajj at least once.
Sheik Abdul-Aziz al-Sheik, the kingdom's grand mufti, said Muslims faced critical challenges, among them accusations of terrorism and human rights abuses and calls for revisions in their school textbooks.
"Oh, Muslim nation, there is a war against of our creed, against our culture under the pretext of fighting terrorism. We should stand firm and united in protecting our religion," he said, speaking at a mosque on the plain of Mount Arafat.
"Islam's enemies want to empty our religion from its contents and its meaning. But the soldiers of God will be victorious," said al-Sheik, the Saudi kingdom's top religious authority.
The faithful called out: "Amen!"
While pilgrims continued their prayers outside the mosque, many held out hands to help others climb the mount, a rugged hill. Men and women, otherwise not allowed to mix in the conservative kingdom, jostled against one another.
At the top, the pilgrims pushed and shoved to get near enough to embrace a sacred pillar. Some paused to photograph the occasion.
"Oh God, I am your obedient servant come to you to ask forgiveness," Moroccan pilgrim Abdull Wahid Boughriba said in a tearful prayer.
Helicopters hovered above the plain — dotted by pilgrims all the way from Mecca to the base of the mount — to guard against the tragedies, mainly stampedes, that have marred the hajj in past years.
Two years ago, 244 people were trampled to death when the crowd panicked during the ritual stoning of the devil, which happens Tuesday.
Saudi authorities, meanwhile, replaced the cover of the Kaba with a new one Monday, an annual ritual at Mecca's Great Mosque. The black cover, called Kiswa, is made of about 658 square yards of silk weighing 1,475 pounds and embroidered with 33 pounds of gold thread. The new Kiswa cost $4.7 million.
The old one is usually cut into pieces and given to Muslim dignitaries visiting the kingdom.
The Kaba, the huge cube-like edifice, is considered the focal point of the hajj. It also serves as the Qibla, or center of the Islamic world toward which all Muslims turn in prayer.
The Quran declares the Kaba was the first place of worship designated by God. Muslims believe that the Kaba was built by Abraham on the foundations of an earlier temple built by Adam, the progenitor of all mankind.