(CNN)"Imagine a world within a world." That is how Hormuz Bana describes the centuries-old community where he lives in Mumbai -- and which is in danger of vanishing.
Located below the Eastern Express Highway, this storied enclave is everything that most of Mumbai is not: idyllic, languid, and devoid of the city's signature traffic.
"Living here has given me a sense of belonging," says the 30-year-old marketing executive.
Bana lives in Dadar Parsi Colony, one of 25 colonies in Mumbai that officials designed solely for Parsis, an ethnoreligious group of Persian descendants in India who follow the Zoroastrian religion.
The Zoroastrians, whose doctrines influenced the principles of Judaism and Christianity, fled from Persia -- modern-day Iran -- to India in the 7th century to avoid political and religious persecution. Over centuries, a thriving community of bankers, industrialists, traders and engineers grew along India's west coast.
But their numbers are dwindling. According to Indian Census data, there were more than 100,000 Parsis in the country in 1941. By 2011, there were fewer than 60,000. And by 2050, experts predict numbers will drop to about 40,000.
As numbers dwindle and the community fights to sustain itself, progressives want to widen the remit for new members. But they face strong resistance from more orthodox Parsis, who believe any dilution of their faith is sacrilegious.
Inside the enclave
Dadar Parsi Colony was established in the mid-1890s after the bubonic plague tore through Bombay, as Mumbai was then known, claiming thousands of lives.
At the time, the city was home to about 800,000 people, and the illness quickly spread through crowded slums. To ease congestion, the city's British colonial leaders expanded Bombay's limits to Dadar, then a low-lying marshland.
Visionary engineer Mancherji Edulji Joshi persuaded British authorities to set aside plots for lower middle-class Parsis, and drew up a blueprint of a model neighborhood, detailed to the type of flowers and trees to be planted on the streets. Joshi was given a 999-year lease for 103 plots.
In Dadar, the colony's leafy streets were laid out in a grid formation, lined by low-rise Victorian apartment blocks.
"He had a rule that no building should be more than two stories high," says Joshi's granddaughter, Zarine Engineer. "Before a single house was constructed, he planted the streets with trees, each street with a different kind."
Jam-e-Jamshed Road -- named after the prominent Parsi newspaper -- still has rows of ashoka trees. Firdausi Road, named after the Persian poet Firdawsi, is dappled with mahogany.
There is a library, a function hall, sports grounds, a seminary, a school, and a temple. The buildings are named after their proprietors: Dina House, Readymoney House and Marker House. It was not uncommon for Parsis' surnames to reflect their line of work.
The Readymoneys, for example, made their fortune by trading opium, which was a ready source of money. Another family, the Sodawaterbottleopenerwalas -- "wala" meaning "of a place of trade" -- most likely made a business of opening soda water bottles. It remains one of the best-known Parsi surnames and there's even an Indian chain of restaurants named after them.
Of all the Parsi colonies in Mumbai, Dadar Parsi Colony remains the largest. It is home to about 15,000 Parsis, roughly 12% of the community's global population.
Every morning, sometimes as early as 4:30 a.m., the colony's fitness enthusiasts power walk up and down the streets. Many of the older residents surface slightly later, perched on their verandas to pry on what's happening beneath them.
Soon, the fishmongers and vegetable sellers make their way to each apartment, selling their daily produce. The garbage collectors dutifully come to collect the garbage, and the launder does the same for clothes. There's an ironing man to collect and drop off ironed clothes, and the knife sharpener visits to sharpen knives.
But over the years, there have been attempts to thwart the community's traditional way of life. Engineer has, time and time again, fought off threats of encroachment on the colony by municipal corporations.
Ninety-year-old twins Mithoo and Mani Contractor, Joshi's cousins, have lived in the colony all their lives.
Joshi's granddaughter, Zarine Engineer, 75, another Dadar Parsi Colony local, sits on the same board of trustees that her grandfather did, the Parsi Central Association (PCA).
The PCA looks after the well being of the colony's residents -- although 99 years later, the PCA's methods have changed. Now, it has a WhatsApp group, in which members voice their complaints -- perhaps a broken street lamp or a pothole -- and Engineer will arrange for it to be fixed.
"When I was a young girl, I would sit beside (Joshi) as he patiently listened to the qualms of the residents," says Engineer. "Some would complain of monkeys entering their house through windows, or a fallen tree, and today I am doing the same."
The apartments are cheap -- and empty
Today, Mumbai's extreme wealth disparity has earned it the moniker of the world's "most expensive slum."
More than half of its residents live in slums with no running water, often just feet from some of the city's most expensive high-rises. The average rent for a two-bedroom apartment in the wider Dadar district costs an average Rs. 145,000 ($1,920) a month.
But rents inside all 25 of Mumbai's Parsi colonies have barely increased in decades. Long-time tenants continue to pay about Rs. 300 ($4) per month, and most are no longer perceived as lower-middle class.
Parsis are one of the most successful and wealthy minority groups in the world. They make up less than 1% of India's entire population, but four Parsis sit on the country's list of top 20 billionaires.
Apartments like the ones in the Parsi colonies -- spacious, well maintained and low in cost -- are hard to come by in Mumbai. Their interiors are a blend of British and Chinese influences, from Victorian motifs carved into oak bed frames to porcelain vases obtained through trade with mainland China.
Rents have remained low because of the Rent Control Act from 1947, which regulates the housing market in Mumbai and limits increase for residents who have been living in the same apartment prior to 1947, said Viraf Mehta, a trustee of the Bombay Parsi Punchayet (BPP).
The BPP owns most of the apartments in the Parsi colonies, including about 3,000 which fall under the act, as the same families have lived in those apartments for generations.
Mehta says the BPP rarely increases rents for newer residents "out of benevolence."
Colony apartments are highly sought after for their unique features and low price. Yet about a quarter of flats in the colonies remain empty, according to Mehta. Many of the occupants have settled overseas, but continue to pay the rent to ensure they don't lose the flat.
"The turnover rate is extremely low," says Mehta. "We have close to 1,000 people on waiting lists wanting a flat in one of the colonies, but there are no vacant houses."
Everyone on the waiting list is a Parsi.
Joshi couldn't afford to build a wall around the colony -- and, as a result, Dadar remains the only Parsi enclave without one. But the lack of a physical wall doesn't mean there aren't barriers to entry for those wishing to join the community.
After the BPP sold three plots to a developer some years ago, in 2009, that developer want to sell apartments on the plot to the highest bidder -- even if they were not Parsi.
The PCA eventually won a six-year battle against the developers, and a court granted a permanent injunction restraining the builder from selling flats inside the colony to anyone who was not a Zoroastrian.
Five years later, the Street Vendors' Act -- a nationwide bill aimed at improving the lives of street vendors -- would have paved the way for street stalls in Dardar colony. Led by Engineer, hundreds of people marched in protest to preserve the colony's heritage.
The plan was withdrawn and the colony's roads remain off limits.
Bana, an ordained Zoroastrian priest, lives in an apartment block built by his great-grandfather. His father grew up there, and his grandmother before that.
"To a layman, it would be very difficult to identify where the colony begins and ends," he says. "But to us, we know each nook and cranny like the back of our hands."
Since the 1940s, the number of Parsis in India has plunged.
According to a study by demographer Ava Khullar, there are several reasons for to this phenomenon. Low fertility is one -- about a third of Parsis don't marry, and the average Parsi woman of child-bearing age has one child, compared to a national average of 2.5 children.
The exclusion of children born to women who marry non-Parsi men in the population figures is also a key reason.
The rule became legally binding following the Petit v Jijabhai case in 1908. Suzanne Briere, a French woman and wife of the Parsi industrialist Ratanji Dadabhoy Tata, wished for her body to be left in Bombay's dokhmas, or Towers of Silence, to be exposed to vultures, per traditional Zoroastrian death rites.
After her marriage, she converted to Zoroastrianism by undergoing an initiation ritual performed by a priest. During the ceremony, individuals wear a sudreh (a sacred muslin tunic) and kusti (sacred thread) for the first time, while reciting prayers, completing their initiation into the faith.
Whether this conversion was permitted was up for dispute, as orthodox Parsis believed being born into the community was a prerequisite for initiation.
Briere took her case to the Bombay High Court, where Justices Dinshaw Davar and Frank Beamon concluded that the Parsi community consists of Parsis who are born of both Zoroastrian parents who profess the Zoroastrian religion; Iranis from Persia professing the Zoroastrian religion; and the children of Parsi fathers by "alien" (non-Parsi) mothers who have been duly and properly admitted into the religion. The legal definition excludes the children of Parsi mothers by "alien" (non-Parsi) fathers.
Years later, the same rules are largely followed. Reformists argue it is sexist and bigoted, while others believe that it is the way things should be. "I think it is our duty to ensure that we keep our race going," says Bana, who married a fellow Zoroastrian.
"I have no opinion on interfaith marriages. But personally, I think these are some things we can do to give back to a community when it has given us so much."
Locked out of the colony
The BPP follows the same 1908 judgment made by Justices Davar and Beamon. If one spouse is non-Parsi, they are not deemed eligible for colony life.
"As far as the BPP is concerned, this is the law of the land," says Mehta. "Whatever my personal beliefs are, I have a duty to uphold the trust deed which is bound by this."
In 2019, Sanaya Dalal, a Parsi woman married to a half-Parsi man and resident of Dadar Parsi Colony, challenged these rules after her five-year-old son wasn't granted membership to the colony's gym for being "a non-Parsi."
"So I'm supposed to explain to my son that he'll have to bow out gracefully, leaving behind his friends and the playground that he loves so much," she wrote in an opinion piece.
Dalal's case caused controversy within the community, with conservative members supporting the rule and progressive members deeming them anachronistic. After some debate, her son remains without membership, and is not allowed to enter the clubhouse unless signed in by a member.
Farzeen Khan, a 29-year-old Parsi woman who grew up in Khareghat Colony, sides with Dalal. "The solution (to the falling numbers) is to be more inclusive," she says.
"We are one of the smallest but wealthiest communities in the country. I think it's time to open our doors and see how we can be more inclusive, rather than cling onto our exclusive identity from yesteryear," says Khan.
Despite their disagreements, Bana, the Zoroastrian priest, says Parsis will find a way to continue their legacy.
"We aren't a community that focuses on the negative," says Bana. "I'm certain we will overcome any hurdle that comes our way, be it interfaith marriages, or extinction."