Chaldoran, Iran - The tents of thousands of pilgrims dot the hillside, the air is heavy with the scent of incense, and the sounds of the church bell toll across the valley.
This is the Armenian Christian pilgrimage marking the feast of the 1st century missionary St. Thaddeus, deep in the northwestern mountains of the Islamic Republic of Iran.
Every summer for the past half-century, thousands of Armenian pilgrims from Iran and beyond have descended on the remote Qareh Kelisa (black church) for three days of worship and relaxation with fellow Armenians.
It may seem remarkable that such a tradition holds strong in one of the world's most strictly Islamic countries, but Iran is home to hundreds of thousands of Armenians and a string of historically important churches.
"This is a gathering point which brings people together in one place. It creates solidarity among Armenians from both inside and outside Iran and is the most important date in the calendar," said Hayk Norouzian, a handicrafts dealer from Tehran.
This year up to 4,000 pilgrims, mainly from Iran, neighboring Armenia, and Arab countries with important Armenian populations like Lebanon and Syria have pitched their tents on the hillside to mark the event.
They filled the church - Iran's most important Christian monument which dates back to early decades of the faith - for the climax of the weekend, a church service attended by the patriarchs of Tehran and Tabriz.
"The most important thing is that in a Muslim nation we have preserved this church," said Ani, 32, a female computer scientist and choir singer.
"In Turkey, some Armenian churches have been ruined. It is a point of pride that in this country we have this church. The government of Iran values it and appreciates it," she said.
The church, built on the site of St. Thaddeus's grave after he was slain by a pagan king, has withstood over one-and-a-half millennia of wars and earthquakes to dominate this landscape.
Its distinctively Armenian pyramidal cupolas and mighty defensive walls perch on a mountain ridge in the north of Iran's West Azarbaijan province, just 25 kilometers (15 miles) from the border with Turkey.
But the pilgrimage is not only about religion - it also offers Armenians separated by national borders the chance to come together and celebrate their culture without any interference.
It is only 9:00 am but the early morning chatter of the pilgrims emerging from their tents is joined by joyful sounds of an accordion which has struck up, accompanied by a drum.
Arms aloft, two other men surround the musicians in a traditional dance, joined immediately by two women who kick their legs and twirl their hands in time to the music.
The authorities allow the Armenians considerable freedom in celebrating the ritual and the Islamic dress rules that everyone normally has to obey in public in Iran are relaxed.
Women walk around in T-shirts without the headscarves that are obligatory everywhere else in Iran, although they cover their heads in church.
"We are free here to make our prayers and do as we wish. The government organizations help us to feel really free. Nobody bothers us here," said Gevork Vartanian, one of two MPs who represent Iranian Armenians in parliament.
It is not possible for Muslims to attend the pilgrimage without a special reason. Checks are carried out by Armenian staff on the only road into the church where local government officials are also in attendance.
Beyond that line, visitors enter, for that weekend at least, a distinctively Armenian Christian world.
"People come here from all over the world for this ceremony. We welcome all Christian people," said Vartanian.
"The authorities carry out this work of separation in order for us to be free," he added.
The campers play Armenian "rabiz" music and have brought copious amounts of food to indulge in one of the most Armenian of passions - the "khorovats" or open-air barbecue.
"What I like is that our youth comes here regardless of whether their main purpose is religious, historical, or social. People get to know one another here," said Rene Ahour, a freelance filmmaker from Tehran.
Iran has always emphasized it gives its Christian, Jewish, and Zoroastrian religious minorities full freedom of worship, although large numbers from these communities have emigrated abroad in recent years.
The presence of Armenians in northern Iran dates back thousands of years and Persian Shah Abbas famously brought hundreds of Armenian craftsmen to his imperial capital of Isfahan in the 17th century.
The entrance to Qareh Kelisa is adorned with pictures of two Armenian patriarchs flanking images of Iran's modern leaders - President Mahmoud Ahmadinejad, supreme leader Ayatollah Ali Khamenei, and late revolutionary leader Ayatollah Ruhollah Khomeini.
But an official message pinned to the church from the Lebanon-based head of the Armenian church, Catholicos of Cilicia Aram I, emphasized the foremost importance of the ritual.
"Our religion and our culture are interwoven together and must be preserved. By being Christian, Armenians have preserved their strength throughout history. This pilgrimage should be looked upon as a duty to keep Armenian unity."