Once a year, large numbers of Muslim pilgrims converge in Saudi Arabia, uniting in religious rituals and acts of worship as they perform the Hajj. While fulfilling a religious obligation, they immerse themselves in what can be a spiritual experience of a lifetime for them and a chance to seek God's forgiveness and the erasure of past sins.

WATCH: New PBS series explores the often-overlooked history of American Muslims

This year, the Hajj has been approaching against the backdrop of a tenuous ceasefire in the Iran war and related tensions and uncertainty in the Middle East.

Earlier in the year, travel chaos from the war ensnared some of the Muslims who were in Saudi Arabia performing "Umrah," often referred to as the lesser or minor pilgrimage. Some were stranded and scrambled to find their way home.

Here's a look at the annual Hajj pilgrimage and its significance to Muslims.

The Hajj is one of the pillars of Islam

The Hajj is the annual Islamic pilgrimage to Mecca in Saudi Arabia and involves a series of religious rituals. It's required once in a lifetime of every Muslim who can afford it and is physically able to make it. Some Muslims make the journey more than once.

It is one of the Five Pillars of Islam, in addition to the profession of faith, prayer, almsgiving and fasting.

The annual Islamic pilgrimage cycles through the seasons

The Hajj occurs once a year during the lunar month of Dhul-Hijja, the 12th and final month of the Islamic calendar year. This year, the Hajj will officially start on Monday.

When the Hajj falls during the summer months, the intense heat can be especially challenging. Amid extreme high temperatures in 2024, more than 1,300 people died during Hajj, according to Saudi authorities. The country's health minister said at the time that the vast majority of the fatalities were unauthorized pilgrims who walked long distances under the sun.

A religious obligation and a spiritual experience

For pilgrims, performing the Hajj fulfills a religious obligation and is also a deeply spiritual experience. It's seen as a chance to seek God's forgiveness, to grow closer to God and to walk in the footsteps of prophets.

Communally, the Hajj unites Muslims of diverse races, ethnicities, languages and economic classes from around the world. It leaves many feeling unity, connection and humility. Pilgrims also show up with their own personal appeals, wishes and experiences.

READ MORE: The Hajj pilgrimage and why it's significant for Muslims

Many pilgrims bring with them prayer requests from family and friends that they would like to be said on their behalf.

Some spend years hoping and praying to one day perform the Hajj or saving up money and waiting for a permit to embark on the trip.

Ahead of the journey, preparations may include packing various essentials for the demanding trip, seeking tips from those who've performed the pilgrimage before, attending lectures or consulting other educational material to prepare spiritually and physically.

Pilgrims perform a series of religious rituals

Pilgrims make the intention to perform the Hajj and they enter a state of "ihram." Being in ihram includes abiding by certain rules and prohibitions. For instance, men are not to wear regular sewn or stitched clothes that encircle the body, such as shirts, during ihram. Instead, there are simple ihram cloth garments for men; scholars say the purpose is to discard luxuries and vanity, shed worldly status symbols and immerse the pilgrim in humility and devotion to God.

A spiritual highlight of the Hajj for many is standing on the plain of Arafat, where pilgrims praise God, plead for forgiveness and make supplications. Many raise their hands in worship with tears streaming down their faces.

READ MORE: Muslims converge at Mount Arafat to worship as Hajj pilgrimage reaches its peak

Other rituals include performing "tawaf," which involves circling the Kaaba in Mecca counterclockwise seven times. The Kaaba, a cube-shaped structure, is the focal point toward which Muslims face during their daily prayers from anywhere in the world.

Among other rituals, pilgrims retrace the path of Hagar, or Hajar, the wife of Prophet Ibrahim, known as Abraham to Jews and Christians. Muslims believe Hagar ran between two hills seven times searching for water for her son.

The Islamic holiday of Eid al-Adha

Eid al-Adha, or the "Feast of Sacrifice," is the Islamic holiday that begins during the Hajj, on the 10th day of the Islamic lunar month of Dhul-Hijja.

A joyous occasion celebrated by Muslims around the world, Eid al-Adha marks Ibrahim's willingness to sacrifice his son as an act of submission to God. During the holiday, Muslims slaughter sheep or cattle and distribute some meat to poor people.