Hundreds of thousands of people have turned out for the biggest party of the year. Hordes of people swarm the city streets; one does not walk but is carried along by the movement of the crowd. The revellers, dressed in colorful festive garb, wildly dance and chant. Some of the males even dress up as women for the occasion and are greeted raucously by the celebrants.

Is it New Year’s Eve in Manhattan, Mardi Gras in New Orleans, or maybe Rio? It is none of the above. Although largely unknown by the Western world, millions of Egyptians each year celebrate the birthdays of Islam’s saints.

Some of these moulidin – which literally means birthdays or anniversaries – are tiny, one-day affairs involving a small sect of devotees who gather at the shrine of their spiritual leader. Other feast days, such as Cairo’s moulidin in honor of the Prophet Mohammed’s grandchildren, El Hussein and Saida Zeinab, attract enormous crowds and last days, even weeks. Today in greater Cairo alone, there are at least 80 religious festivals.

One of Egypt’s biggest festivals honors the early 19th century religious leader of Luxor, Yussef el Haggag. Abu Haggag – Abu means father in Arabic – was renowned for his wisdom. Even Mohammed Ali, the father of modern Egypt, sought the sheikh’s counsel.

This moulid, held every year one month before the holy month of Ramadan, attracts hundreds of thousands of pilgrims to the city near the ancient Valley of the Kings in Upper Egypt.

In most cases, the actual date of the saint’s birthday is unknown and relatively inconsequential. Like the Haggag moulid, the celebrations are often planned seasonally, or to coincide with a particular day of the week. For example, the closing ceremonies for the El Hussein and Saida Zeinab moulidin are always held on Tuesdays.

Most of these religious festivals begin with a parade called a zaffa. The procession winds its way through the streets until it reaches the mosque of the honored saint In Luxor’s moulid, the participants are divided into three groups, which correspond with the city’s major professions: fishermen, butchers and carriage drivers. Each group constructs its own “float”; in the fishermen’s case, the men paint a small boat in bright colors, load it up with smiling children, and haul it around town in a horse-drawn wagon. As it sails by, the crowds pelt the children with candy and peanuts.

In the early days of the moulid, the procession bordered on the exotic and the dangerous. The Whirling Dervishes, a Muslim sect, performed their entranced dance, worked tricks with poisonous snakes and scorpions, swallowed broken glass and set themselves aflame. Today, these performers are rarely seen outside Turkey, their home.

The modern moulid is still a glorious, overwhelming sight. The revellers make several sikr circles, where they sway rhythmically and chant “Allah.” Others play the lute, the hand drums, the castanets or simply sing along. Further away from the crowd, partygoers watch a traditional Egyptian horse dance, accompanied by a band. The horses lift their hooves in time to the music, executing the difficult moves in tandem.

At the great moulidin of El Hussein and Saida Zeinab in Cairo, the celebrations escalate in intensity. The El Hussein festival lasts up to a week and attracts nearly a million people by the closing ceremonies. The Saida Zeinab moulid runs even longer and attracts pilgrims from all over the Muslim world.

The thousands of pilgrims who flock to Cairo from the countryside erect tents of colored cotton and canvas – their temporary homes. Gas stoves are lit, endless pots of tea are brewed and food prepared.

The poorer pilgrims, however, find a barren spot on the street to sit or sleep. Meanwhile hordes of people trample on their tiny plots. Giving alms to the poor is one of the five pillars of Islam and is thus an important feature of the moulid. Some pilgrims, particularly members of the Sufi brotherhood, open their tents to anyone in need of a meal or hot tea.

By the time the final ceremonies arrive, the circles of chanting worshippers move faster and with great fervor. As the tempo of the music increases, the participants strive to reach a trancelike state. When their souls rise above earthly matters to join Allah, the world’s greatest birthday party comes to an exuberant end.

Jennifer Reidy and Tom Stevens lived and worked in Egypt; they now work from Connecticut.