Atop a rocky hill southeast of Tehran sits the shrine of Bibi Shahrbanu, a Persian princess who was the daughter of the last Sassanian king of Iran. Following the Islamic conquest, she is said to have married Imam Husain, the grandson of Prophet Muhammad (PBUH).

When Imam Husain was killed at Karbala by the corrupt caliph Yazid — a battle that has become a seminal moment in the history of Islam — Shahrbanu fled and sought refuge further east.

The entrance to the Bibi Shahrbanu shrine.

Pilgrims rest and chat below Bibi Shahrbanu's shrine.

The legend goes that when she arrived at the mountain, her enemies were close behind her; at the mountain’s base she prayed for deliverance, and the rocks opened up and took her in, protecting her from being enslaved by her husband’s murderers.

The legend has long attracted Iranian pilgrims to the shrine.

Shahrbanu perfectly brings together two key parts of Iranian identity: the Persian past and the Muslim present.

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These days, if you visit the shrine you’re just as likely to encounter Pakistani or Indian pilgrims as you are Iranians.

On a recent visit, I found a large Pakistani tour group in the majority among smaller numbers of Iranian and Iraqi pilgrims.

A Pakistani visitor I spoke to said the tour had driven overland from Karachi to visit the major shrines at Mashhad and Qom. They were ending their trek across Iran’s holy sites at Bibi Shahrbanu’s shrine.

These flows of pilgrims are part of a growing network of Muslim shrine tourism that connects Iran and the countries around it, especially Pakistan, India, Iraq, Lebanon and the Persian Gulf.

The courtyard of the Bibi Shahrbanu shrine.

The pilgrimages are focused on the shrines of the 12 Shia imams. Although most of the tombs are in Iraq, some are in Iran, and as the latter is safer and easier to access, it has become a major centre for pilgrimage.

The main sites are Mashhad, which hosts the tomb of Imam Reza, the eighth Shia imam, and Qom, which hosts his sister’s tomb, along with smaller tombs of the relatives of the 12 imams in Tehran.

Many tours visit both Iran and Iraq in one trip, while others concentrate solely on Iran.

Two pilgrims from Iraq look out from above the Bibi Shahrbanu shrine toward the city of Reyy, just south of Tehran, Iran.

Pilgrims rest and pray in the room around Bibi Shahrbanu's tomb, located to the left of the picture.

Although the majority of pilgrims are Shia, many Sunnis come too. This is especially true for India and Pakistan, where the Shia imams are historically revered by many Sunnis as well.

Signs of the South Asian pilgrimage boom are visible in any Iranian shrine city. In Qom’s old city, Urdu signage competes with Persian and Arabic.

Twenty million pilgrims visit Qom every single year. While the majority are Iranian, they are joined by Muslims from both East and West.

Persian cosmopolis

When we think of cosmopolitanism, we often think of places like Dubai, where people from different countries come for work — but in Iran, there is a shrine cosmopolitanism that draws together worshippers from across the world.

Pilgrims from both Pakistan and India come, meeting each other in bazaars and mosques, and they in turn meet Iraqis, Lebanese, Afghans and many others.

While in Dubai all these people might be around, the neoliberal economic structure and stratification of society between rich and poor segregates national and economic groups.

The courtyard of Shah Abdol Azim shrine in Reyy, an ancient town in southern Tehran that hosts the Iranian capital's largest shrine.

Yet all these groups mix freely in and around the shrines, haggling over prices together, trying new foods in restaurants and checking out the devotional icons for sale at the local bazaars.

Iranian-style paintings and depictions of Islamic holy figures have become increasingly popular among Shia communities elsewhere. This is no doubt furthered by the many souvenirs pilgrims bring home with them.

For pilgrims from countries like Pakistan, Afghanistan, Iraq and Bahrain, where Shia communities often feel under siege due to violent persecution, a visit to Iran can feel like a breath of fresh air.

Worshippers pray inside the Fatima Masoumeh shrine in Qom. Her tomb can be seen in the background. Like all shrines in Iran, the space is divided exactly down the middle into men and women's sections.

As pilgrims tour Iran, they see a different political system: a strongly-centralised Islamic Republic where the highways are well-developed, and security and safety are ever-present and tightly-regulated.

Due to the fact that Iran is one of the world’s few Shia-majority countries, Shias of neighbouring countries are often associated with Iran. As a result, they often have to craft identities and how they present themselves locally with Iran in mind.

Pilgrimage is one of the few times Shias are able to actually see the country for themselves. A visit to Iran isn’t just a chance to pray at the shrines of holy women and men; it’s also an opportunity to evaluate the positives and negatives of the Iranian political model.

Fatima Masoumeh shrine in Qom houses the tomb of the sister of the eighth Shia Imam Reza. The shrine is the largest and most important shrine to a female saint in Iran, receiving around 20 million pilgrims yearly.

The rising popularity of samosas as Iranian fast food attests to the boom in South Asian pilgrimage, but also points to the longer history of ties that bind these countries.

Locally, samosas are known as sambousak. Although South Asians tend to think of samosas as quintessentially local, historians believe they actually come from Central Asia, introduced first to the Middle East and subsequently from there to India.

In Iran today, this history is not well-known; most people think of samosas as typical Arab-style food from the Persian Gulf coast, along with falafel.

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But because South Asians also love samosas, the main streets of Qom are now full of shops selling this beloved transnational snack food.

The samosa is a reminder that Iran has long been closely connected to South Asia.

This connection is not just through Islam — which entered South Asia through Iran — but also a long history of Persian language and culture, which connected these two regions and Central Asia together.

Scholars have called this shared culture the Persian Cosmopolis. For five centuries until the arrival of the British, Persian was the lingua franca of India.

Iraqi pilgrims take a selfie at the golden door to Fatima Masoumeh's shrine in Qom.

In Iran and Central Asia, just like in South Asia, there have always been many languages — but Persian was the language and culture that tied people together irrespective of what they spoke at home.

Today, about half of Iranians grow up speaking a language other than Persian (Azeri Turkish, Kurdish, Baluchi, Arabic, Turkmen and so on) — but Persian remains the language that ties everyone together.

But this Persian Cosmopolis has much deeper roots than Islam. Bibi Shahrbanu’s tomb outside Tehran highlights this fact.

Like many others across Iran, the shrine is thought to have previously been a Zoroastrian fire temple dedicated to the goddess Anahita, for whom a legend similar to Bibi Shahrbanu’s also exists.

Meanwhile, Zoroastrianism — which was the state religion of Iran before Islam — shares many features with early Hinduism.

For example, Ahura Mazda is considered God in the Zoroastrian holy texts, the Avesta, but is associated with evil in the Hindu Vedas. In Zoroastrianism, spiritual beings called daevas are associated with evil, while in Hinduism, devas are associated with good.

This overlap points to a shared origin from which both religions departed.

The golden dome of the Fatima Masoumeh shrine in Qom. Shrines of the 12 Shia imams and their descendants tend to be topped by a large golden dome, part of a shared transnational religious aesthetic.

This is also evidenced by the fact that Persian and Hindi diverged from the same language; as a result, Sanskrit and Old Persian share both grammar and vocabulary, and many similarities persist in their modern descendants.

More recently, Zoroastrians have long maintained close networks and ties between Iran and South Asia. Over the last two millennia, thousands of Persian Zoroastrians from Iran and Central Asia have migrated to what is now India and Pakistan, and today they are known as Parsees or Iranis.

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Their presence — as well as that of their fire temples in cities like Mumbai and Karachi — are a constant reminder of South Asia’s longstanding and continual links with Iran.

After Zoroastrianism ceased to be Iran’s state religion and most Zoroastrians gradually converted to Islam, they took their holy sites with them. Many fire temples were converted into shrines over time, and places that had been sacred for centuries retained their sense of holiness, albeit with different names.

This process of converting Zoroastrian temples to Islamic shrines is not unique to Islam. The major Christian holy sites in Jerusalem and Bethlehem in Palestine, for example, were built atop pagan Roman temples that were demolished as part of the conversion of the Empire to Christianity.

Shoppers inside Qom's historic bazaar, where pilgrims search for souvenirs, devotional icons, and local sweets famous to the city.

And many Hindu sites, likewise, were previously local deities that were taken over by Brahminical traditions. Over time the memory of the initial gods was lost or deemphasised as the site’s association with a Brahminical holy figure came to be more prominent.

More commonly, different people continued worshipping at these sites for different reasons; a common sight not only in South Asia but in Iran as well, where numerous shrines are shared between Muslims, Jews, Christians and Zoroastrians.

And let’s not forget that Zoroastrianism itself was a state religion, meaning many of its shrines were likely built atop previously existing pagan sites.

At Bibi Shahrbanu, the multiple layers of this shared past — Zoroastrian, Muslim, Persian — come together.

Bibi Shahrbanu's shrine.

South Asian pilgrims have been coming to Iran for centuries. Based on my research in the British Library’s historical archives, I have found that the British consul in Mashhad estimated that about 100 Indian pilgrims visited the city every month in the 1920s.

But with the increasing ease of travel and the vast improvement of infrastructure in Iran since the 1979 Revolution, it is easier than ever for millions of South Asian pilgrims to make their way to Iran.

Sitting on tour buses making their way overland from Karachi to Tehran, pilgrims reconnect lands torn apart from each other by colonialism.

Whereas for so long Iranians and South Asians were more likely to meet each other in Dubai or the West, today the streets of Qom, Mashhad or Tehran are far more likely sites for this encounter.

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