Nearly 1.5 million pilgrims have converged on western Saudi Arabia for the annual hajj where new measures aim to prevent a recurrence of last year's stampede which killed around 2,300.
The stampede legacy has contributed to renewed tensions between Saudi Arabia and its regional rival Iran, which is not sending pilgrims for the first time in nearly three decades.
While the main rites of the six-day event begin on Saturday, pilgrims have already been swirling around the holy Kaaba at the Grand Mosque in Mecca, a procession that continues day and night.
It is one of the first rites of the pilgrimage, which is among the largest religious gatherings in the world.
The hajj is one of the five pillars of Islam, which capable Muslims must perform at least once, marking the spiritual peak of their lives.
Rich and poor alike come dressed in the same white garments.
"We don't come here with fear in our hearts," said Naouri Abdelkarim, 50, of Casablanca, Morocco.
Death can come at any time, pilgrims say, and for Lawan Nasir, 45, that meant there was no reason to avoid the hajj even though he lost a cousin in last year's stampede.
"The pains have not dulled a bit," but it would be "silly" to stay away, the Nigerian told AFP.
In one of several safety measures implemented after the stampede, access to the Kaaba is suspended during prayers, and the walk around it is stopped to avoid overcrowding.
The Kaaba is a black cubic structure that Muslims across the globe face while they pray.
Security has also been reinforced around Islam's holiest site, where officers in red berets and camouflage uniforms man green plastic barricades to control the crowd.
During the main weekly Friday prayers, the white-clad throng made the area around the Kaaba resemble a snow-dusted field from above.
Worshippers overflowed into surrounding streets shut to allow access for hundreds of thousands of people as a helicopter monitored the scene.
Pilgrims have also been told to follow the rules.
"They said not to stray from our group, not to linger when buses arrive and depart, and to properly respect the designated routes," said Rasha Mohammed, 36, of Alexandria, Egypt.
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With temperatures of 43 Celsius (109 Fahrenheit) as they marched, some pilgrims seemed faint. They carried water and tried to help each other under the unyielding sun.
- 'Absence of transparency' -
The kingdom has begun issuing pilgrims with identification bracelets, after some foreign officials expressed concern about difficulties in identifying the stampede dead.
Each bracelet carries a bar code readable by smartphone. It holds data including the pilgrim's identity, nationality, and place of lodging in Mecca, the vice secretary of the ministry of hajj and umrah, Issa Rawas, told AFP.
He said: "The aim is to equip all pilgrims" from abroad, who are expected to number more than 1.4 million, according to the latest official figures.
The rest of the numbers will be made up of people from inside Saudi Arabia.
Zakou Bakar, 50, a pilgrim from Niger, said the bracelet was reassuring.
"If I die or if there are problems -- of course we hope not -- but if it does happen I know I will be identified," he told AFP.
Despite the Saudi steps, the head of Iran's Hajj Organisation, Said Ohadi, on Friday asked how the kingdom could invite the world's Muslims and not allow questions about the security measures to be raised.
Absent from this year's hajj are tens of thousands of Iranians after talks between Tehran and Riyadh on logistics and security fell apart in May.
Thousands of people in Tehran on Friday protested their country's absence from the pilgrimage.
Iran said 464 nationals died in last year's crush, the highest number of fatalities reported by any country.
Jane Kinninmont, deputy head of the Middle East and North Africa programme at Chatham House, a London think tank, said the stampede exposed "clearly some big organisational failings, to say the least".
There was also "an absence of real transparency" about what went wrong, she said.
Saudi Arabia has an economic stake in ensuring pilgrims' comfort and safety.
As part of efforts to diversify its oil-dependent economy, the kingdom wants to foster a year-round religious tourism sector relying on millions who perform the umrah, or lesser pilgrimage.