More than 1.8 million gathered from sunrise at the hill and a vast surrounding plain known as Mount Arafat, about 15 kilometres (nine miles) from Mecca.
Against a backdrop of distant, higher peaks, they squatted, stood, or climbed steps built into the hill while reciting ritual incantations.
From a distance, the hill appeared a snowy white, as male pilgrims wear a seamless two-piece white garment, ihram.
It symbolises a state of purity and emphasises their unity regardless of social status or nationality.
Women wear a loose dress, typically also white, but some like Soumaya, 30, of Mali are in traditional attire, in her case an orange robe.
“We feel at ease and are totally benefiting from our pilgrimage,” she said, giving only one name.
“Everything is very well organised,” added her friend, Khadija Bechir, 23.
Pilgrims come from every corner of the globe, but Indonesia — the most populous Muslim nation — has the largest quota.
Official figures issued late Saturday said the total number of pilgrims exceeds 1.8 million, with more than 1.3 million arrived from outside the kingdom.