The enemy no one saw coming at the Sixty Dome Mosque
The Sixty Dome Mosque has survived centuries of storms and empires, but climate change is now driving a quieter, more destructive force from within
Every Friday morning, Mohammad Helal Uddin, an imam, walks the same path his predecessors have walked for six centuries—past the pond, through the arched eastern doorways, and into the cool, dark belly of the Sixty Dome Mosque in Bagerhat.
He has done this for thirty years. He knows every pillar, every dome, every shadow.
And lately, he has come to know something else: a white, crystalline crust creeping across the ancient brickwork like a slow tide. "I have been noticing for six or seven years now," he says, "that the walls are getting damp, turning a green colour." At night, he leaves an electric lamp burning inside the mosque—not for prayer, but to keep the damp at bay. It is a quiet, almost absurd act of resistance. A single bulb against the ocean.
For six centuries, the Sixty Dome Mosque has outlasted empires, floods, and jungle. Now it faces an enemy it was never built to fight.
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The Shat Gambuj Masjid, or the Mosque of Sixty Domes, has stood in the south-western corner of Bangladesh since the mid-fifteenth century. Built by the Turkish general and Sufi saint Khan Jahan Ali around 1459, it is the largest mosque from the Bengal Sultanate period in all of South Asia—a vast hypostyle hall of 60 stone pillars supporting 77 low, curved domes. It is a UNESCO World Heritage Site. It has been swallowed by the jungle and excavated again. It has survived cyclones, colonial neglect, and centuries of monsoon. What it was not built to survive—what nobody in the fifteenth century could have imagined—is the particular slow violence of a warming planet: rising seas, intensifying storms, and, most insidiously, salt.
A city carved from tide and forest
To understand what is happening to the mosque, you have to understand where it sits. Bagerhat lies in Bangladesh's south-western delta, a landscape of rivers, tidal channels, and low, waterlogged earth just north of the Sundarbans, the world's largest mangrove forest. This is land that the sea has always contested. Khan Jahan Ali literally carved the city of Khalifatabad out of mangrove forest, establishing reservoirs, roads, and dozens of mosques on ground that sits barely above sea level. It was, from the beginning, an act of audacious reclamation.
For centuries, the geography was manageable. The Sundarbans acted as a buffer, the rivers ran their old courses, and the salt stayed in the sea where it belonged. But the sea is no longer staying where it belongs. Global warming has pushed sea levels steadily upward in the Bay of Bengal. Cyclones like Sidr in 2007, Aila in 2009, and Amphan in 2020 have grown stronger and more frequent, driving storm surges deep into the delta. And with each surge, saltwater pushes further into the soil, further into the water table, further into everything.
The numbers from Bangladesh's Soil Resource Development Institute tell the story in blunt statistical terms: in 1973, about 800,000 hectares of coastal land were classified as saline. By 2009, that figure had crossed one million. It has not stopped growing since. Bagerhat sits squarely within this expanding salt frontier.
What salt does to a 600-year-old brick
The mechanism of destruction is called efflorescence, and it is devastatingly simple. Saltwater, whether from the soil, groundwater, or the increasingly salty air itself, seeps into porous building materials.
As it moves through the brick, water carries dissolved salts. When the water evaporates near the surface, the salts are left behind. They crystallise. They expand. And with each cycle of wetting and drying, they push a little harder against the material around them, widening microscopic cracks, loosening mortar, and slowly, patiently, eating the brick from the inside out.
Khandoker Mahfuz ud Darain, a professor of architecture at Khulna University who has been studying this phenomenon since 2017, has watched it happen in real time at the Sixty Dome Mosque. Three sides of the mosque were renovated about a decade ago with specially made bricks intended to resist this process. The results have been troubling. "Salt has been observed in these reformed places," Darain says. "The new bricks have a higher salt rate than the old ones on the north side."
The one side that was not renovated, and where the original medieval brickwork still stands, tells a different story. The old bricks, it seems, were better prepared for their environment than their modern replacements.
Salt is not the only weapon in the climate's arsenal. Rising temperatures are causing the brickwork to expand and contract with increasing extremes, opening cracks in the structure. Through those cracks pours the monsoon rain, which is growing heavier and more erratic, carrying more saltwater deeper into the walls. The domes themselves, those magnificent low curves that have defined the Bagerhat skyline for six centuries, now show salt deposits on their exteriors. The green discolouration that Helal Uddin notices on his walls is biological—algae and fungi finding purchase in the newly damp surfaces. The mosque is, in a very real sense, being colonised.
The hardest part: it is not just one mosque
Walk beyond the Sixty Dome Mosque and the same story repeats itself in smaller, quieter registers. The Nine Dome Mosque, the Bibi Begni Mosque, the Ranbijoypur Mosque, the Chunakhola Mosque—all are showing the same symptoms.
"In this vicinity, all are in the same condition. The biggest problems are in the Sixty Dome and Chunakhola mosques," says Ahmed Ali, a local resident who has been a regular visitor to these sites.
"These mosques are not just ours; they are the wealth of the world. The government and the world community must pay attention," he adds in a rather helpless tone.
UNESCO, in its own assessment of the site, has acknowledged that the extreme salinity of the soil and atmosphere poses a potential threat to the physical integrity of the site's attributes, and has flagged that interventions are needed with particular urgency at the Shaitgumbad Mosque. The language of the international heritage bureaucracy is careful and measured. The reality on the ground is less so.
"Salt has been observed in these reformed places. The new bricks have a higher salt rate than the old ones on the north side." — Khandoker Mahfuz ud Darain, Professor of Architecture, Khulna University
In 2019, the international heritage documentation organisation CyArk travelled to Bagerhat with a specific and sobering mandate: to create a precise, three-dimensional digital record of the Sixty Dome Mosque, the Nine Dome Mosque, and the Chunakhola Mosque—not as a tourist exercise, but as an act of archival insurance. The data collected was meant to give conservators a baseline against which to measure future deterioration, and to allow the quantification of efflorescence patterns that the eye alone cannot track. It was the kind of project you undertake when you are not entirely certain the thing you are documenting will still be there in its current form in a generation.
An uncertain inheritance
There is a particular kind of grief in watching something ancient accelerate towards ruin. The Sixty Dome Mosque has already outlasted the civilisation that built it, the sultanate that commissioned it, the language in which its prayers were first recited, and the forest from which its building materials were fired. Six hundred years of human history have washed around it and left it standing. But human history, specifically the industrial history of the past two centuries and the carbon it has pumped into the atmosphere, may accomplish what no cyclone or jungle could.
Darain is clear-eyed about what is required. "Normal renovation will not work at these mosques," he has said. The conservation strategies that served the site for decades—the patching and re-pointing and careful replication of original materials—were designed for a stable climate. They were not designed for a climate that is actively changing the chemical composition of the soil and air around the buildings they are meant to protect.
What is needed now is something more fundamental: new research into salt-resistant materials that can still honour the original aesthetic, better drainage systems, active monitoring of salinity levels, and, above all, the international funding and political will to act before the losses become irreversible.
The World Heritage designation that was meant to be the mosque's greatest protection has not, on its own, been enough. "Though financial efforts have been made to address the conservation problem derived from salinity," UNESCO's own documentation acknowledges, "this has not been comprehensively solved and deterioration has continued."
Helal Uddin, the imam, has delivered his Friday sermon in that vast, columned hall for thirty years. He has prayed beneath those domes in the monsoon and in the dry season, in the cool of December and the furnace of April. He has watched the walls change. He keeps his lamp burning. And he hopes, as the khatib of a mosque hopes, and as a man watching something irreplaceable slowly dissolve hopes, that someone, somewhere, will pay attention before the salt takes the rest.
Note: The Historic Mosque City of Bagerhat was inscribed as a UNESCO World Heritage Site in 1985. It remains an active place of worship today.
