Every year, millions of pilgrims come from around the world to pay homage at the Muslim holy city of Mecca in Saudi Arabia, which is believed to be the birthplace of the Prophet Muhammad. Every able-bodied Muslim is expected to make the trip at some point in the lives, and those who have taken the hajj, as the pilgrimage is known, can add the honorific hajji to their names. Here, we take a look at Mecca as this year's hajj, which officially begins Wednesday, kicks off.

The hajj begins at a way station just outside Mecca known as the Miqat, where visitors put on ceremonial seamless garments and recite a prayer. The pilgrims then walk to the Kaaba -- the most sacred site in Islam -- and walk around it seven times repeating prayers. Above, an aerial view shows Muslim pilgrims gathering at the Grand Mosque in Mecca on Oct. 22.The Kaaba is the square, black building inside the mosque.

Above, Muslim pilgrims perform their prayers in the Grand Mosque on Oct. 22. Over two million Muslims from around the world are predicted to flood the Saudi city of Mecca.

Muslim pilgrim women pose for picture after the end of evening prayers at the Grand Mosque in Mecca, on Oct. 23.

While on the hajj, male pilgrims are expected to wear the ihram, a seamless, white tunic, and women to wear a hijab, or head scarf. As a pilgrim, participants are not allowed to shave, clip their nails, have sex, argue, kill animals, or carry weapons. Above, people wait for the start of prayers in the Grand Mosque on Oct. 22.

The Abraj al-Bait towers, also known as the Mecca Royal Hotel Clock Tower, seen from Jabal al-Noor, or the "Mountain of Light," which overlooks  Mecca, on Oct. 21.

Hajj pilgrims come from around the world, many traveling great distances. Some airlines even offer special hajj packages. Above, relatives wave as Thai Muslim pilgrims depart for the hajj at Narathiwat airport in southern Thailand on Sept. 20.

Nigerian hajj pilgrims wait outside the arrival hall of Mallam Aminu Kano International Airport shortly after their arrival in Medina on Sept. 26. This year, Saudi Arabia denied entry to some 1,000 Nigerian woman because they were not accompanied by men, leaving many stranded at the Jeddah airport. About 171 of the women returned home to Nigeria on a flight the same day.

As Mecca experiences an influx of foreigners, the Saudi Arabian government has insisted that pilgrims will not be affected by the instability in Syria or recent outbreaks in violence in Lebanon. Above, pilgrims gather at night in the Grand Mosque on Oct. 22.

Still, Saudi authorities are on high alert. Saudi Interior Minister Prince Ahmad bin Abdul Aziz continues to pledge that the security in place is adequate to ensure an uneventful hajj. Above, Saudi Interior Ministry special forces parade on Oct. 20 in Mecca.

But even without unrest,  this year's hajj has observers worried. Epidemiologists recently raised alarm about the influx of so many travelers into Saudi Arabia just after the discovery of a new virus there. Not much is known yet about the disease, but it's related to the same virus that caused the 2003 SARS outbreak. Above, a Muslim pilgrim leaves the Grand Mosque with his daughter after performing the evening prayers on Oct. 22.

Muslim pilgrims perform evening prayers in the Grand Mosque on Oct. 22.

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