The hajj reached its high point Sunday when Muslims from across the world converged on a stony hill in Saudi Arabia, a year after the worst tragedy in the pilgrimage's history.
In a bid to prevent last year's disaster, Saudi authorities deployed drones to watch over the nearly 2 million pilgrims as they ascended Mount Arafat at the climax of the hajj on Sunday.
Last year's deadliest disaster was one of the worst to befall the annual Muslim rite in decades.
Authorities have deployed drones to reinforce a network of electronic surveillance of the crowds that would alert authorities to intervene quickly if necessary.
According to Riyadh, more than 800 pilgrims were crushed to death last year, though counts by countries of repatriated bodies showed over 2,000 people may have died, more than 400 of them Iranians.
Despite last year's catastrophe, pilgrims climbed the craggy hills outside Mecca where Islam holds that God tested Abraham's faith by commanding him to sacrifice his son Ismail and the Prophet Mohammed gave his last sermon.
In stifling heat they chanted a traditional hajj incantation, "here I am answering your call, O Lord," spending the most important day of the annual rite in prayer and reading from the Koran.
"I have prayed to God to have mercy on us, give us relief and resolve Syria's crisis," said Um Fadi, wearing a traditional long black embroidered dress and head scarf native to her home in southern Syria.
Saudi Arabia has said that 1.85 million pilgrims, most of them from outside Saudi Arabia, have arrived for the annual pilgrimage, which capable Muslims, who can afford the journey, must perform at least once, marking the spiritual peak of their lives.
Pilgrims flocked to Arafat from early morning after spending a night of meditation and introspection in the tent city of Mina, which marked the first leg of their five-day Hajj.
After sunset, the throng moved aboard buses to nearby Muzdalifah, in preparation for the first hajj stoning ritual.
"The feeling is indescribable. I am very happy and I hope everything goes well until the end of hajj," said Saudi pilgrim Bashar Aatabi, 30.
He was eating chicken and rice on the ground with his friends after reaching Muzdalifah.
At midday prayers in Mount Arafat, hundreds of thousands of people prostrated themselves, men and women side-by-side, in wide alleys that run between prefabricated pilgrim lodgings.
"It's beautiful to see the Muslims of the world pray together here," said Indian pilgrim Mohammed Arafan, 40.
A teenage Indian pilgrim, who gave her name only as Janifa, said she was "lucky, and very grateful" to have made the pilgrimage with her parents.
From a distance, the Arafat hill appeared a snowy white because of the seamless two-piece white garment, ihram, worn by male pilgrims. Women also usually wear white.
They come from every corner of the globe for the hajj, but Indonesia, the most populous Muslim nation, has the largest contingent with more than 155,000 pilgrims.
Trucks loaded with bottled water were stationed throughout, and pilgrims doused themselves.
Empty bottles and leftover meals littered the ground as ambulances patrolled.
At Muzdalifah, half way between Arafat and Mina, pilgrims gather 49 pebbles for Monday's symbolic stoning of the devil, the last major rite of hajj.
It coincides with Eid al-Adha, the feast of sacrifice marked by Muslims worldwide.
King Salman arrived in Mina to ensure pilgrims can "perform their rituals easily conveniently and safely", the Saudi Press Agency said.
He was also being briefed on the movement of pilgrims between the holy sites.
Additional safety measures have been implemented this year including the distribution of bracelets which store pilgrims' personal data. Roads have also been widened in the Jamarat area, newspapers reported.
Pilgrims told AFP they feel safe and have noticed organisational improvements.
"The Saudis organise everything for us. We are truly at ease here in Arafat," Youssef al-Mehri, 24, of Oman said with a prayer rug slung over his shoulder.
Despite the safety and security measures which Saudi Arabia says it has taken, Iran has angrily questioned the kingdom's custodianship of Islam's holiest places.
Iran last year reported the largest number of stampede victims, at 464, and its 64,000 pilgrims are excluded for the first time in decades after the regional rivals failed to agree on security and logistics.
Hundreds of thousands of Iranian faithful held an alternative pilgrimage on Saturday in the Iraqi Shiite holy city of Karbala, according to an official at the shrine of Imam Hussein.
Saudi Arabia on Sunday said it had launched a television channel to broadcast the hajj rituals in the Persian language, also known as Farsi, spoken in Iran.