More than two million Muslims have gathered at the sacred hill of Mount Arafat in Saudi Arabia for a day of worship and reflection, on what is considered the climax of the Islamic hajj pilgrimage.

Many had tears streaming down their faces as they raised their hands in worship on the slopes of the rocky hill where the Prophet Muhammad delivered his final sermon 1,400 years ago, calling for equality and unity among Muslims. Thousands had walked there through the pre-dawn darkness.

As one of the largest religious gatherings on Earth, this second day of the hajj is often the most memorable for pilgrims. They stand shoulder to shoulder with Muslims from around the world, all considered equal in Islam before God, seeking mercy, blessings, good health, bounty and healing.

Hundreds of thousands of Muslim pilgrims pray outside Namira Mosque in Arafat
Hundreds of thousands of Muslim pilgrims pray outside Namira Mosque in Arafat (Amr Nabil/AP)

More than 1.8 million people from over 160 countries are in Saudi Arabia this year to perform the hajj, according to Saudi officials. Around 200,000 more are Saudi residents or citizens.

The five-day hajj is required of all Muslims once in their lifetime, if they are financially and physically able to make the demanding pilgrimage.

Because the Islamic calendar is a lunar one, the time of year when the hajj takes place varies, and when it falls in the hot summer months, temperatures can soar to over 38C.

Most pilgrims save for years to afford the trip, which takes them to Islam’s holiest sites to perform a series of ancient rituals that date back thousands of years.

While following a route the Prophet Muhammad once walked, Muslims trace the rites of hajj back to the prophets Ibrahim and Ismail, or Abraham and Ishmael as they are named in the Bible.

Muslim pilgrims pray on the Mountain of Mercy
Pilgrims pray on Mount Arafat (Amr Nabil/AP)

The oldest pilgrim this year is 103-year-old Noah Lanai from Thailand, according to Saudi Arabia’s state-run media. She arrived with her son and was quoted in local media saying she had long dreamt of performing the hajj and praying in Mecca.

Muslims believe the hajj is a chance at atonement and an opportunity to erase past sins. It is also a chance to pray for unity and peace among Muslims as conflicts rage in Syria, Yemen and Libya, and Muslim minorities face increased threats around the world.

After spending the day in prayer on Mount Arafat, pilgrims will head towards an area called Muzdalifa, about 5.5 miles west.

In Muzdalifa, pilgrims will rest and pick up pebbles to be used for a symbolic stoning of the devil and casting away of evil. This takes place over three days in Mina, about 12 miles east of Mecca.

The final days of hajj coincide with Eid al-Adha, the festival of sacrifice celebrated by Muslims.