If you visit the ruins of Firozshah Kotla on a Thursday afternoon, you will see something most guidebooks don't mention. Slipped into the cracks of the 14th-century walls, folded into the niches of forgotten chambers, are sheets of paper. Some are handwritten, some are photocopies. Many have a name and an address on the back. They are letters — and they are not addressed to anyone alive.

The recipients, according to those who write them, are djinns.

A fort built for an emperor, repurposed for the unseen

Firozshah Kotla — properly, Kotla Feroz Shah — was the citadel of Firoz Shah Tughlaq, the third ruler of the Tughlaq dynasty, who founded the fifth city of Delhi in 1354. He moved his capital here from Tughlaqabad and built the fort on the banks of the Yamuna. The walls he raised still stand. The mosque inside, the stepwell, the pyramidal platform crowned by an Ashokan pillar that Firoz Shah dragged from Topra and re-erected here — they are all visible, weathered, walkable.

What no plaque inside the monument explains is why, every Thursday evening for at least the past fifty years, hundreds of Delhi residents arrive carrying incense, sweets, and letters.

“The djinns are old. They listen carefully. You must write clearly, in good handwriting, what you need. Then you leave the letter and you go.”

That is what a woman from Old Delhi told the anthropologist Anand Vivek Taneja, whose book Jinnealogy documents the practice in detail. Taneja spent years at the site. He found that the letters are written most often by Muslims, but also by Hindus, Sikhs, and Christians. They ask for jobs. For medical recoveries. For visas. For a marriage to work out, or for one to end. They thank the djinns for prayers that have already been answered.

Why Thursdays

Thursday — Jumeraat — is the eve of the Friday prayer in the Islamic calendar, and across South Asia, Thursdays carry a particular weight at Sufi shrines. The practice at Firozshah Kotla is not formally Sufi. There is no living saint here. No grave. No order to follow. And yet the rhythm — that thinning of the veil between the seen and the unseen on a Thursday evening — has migrated to this place.

There are several theories about how it began. One version, repeated by older visitors, holds that the practice intensified during and after the 1977 Emergency, when slum demolitions across Delhi displaced thousands of working-class residents. Many had nowhere to go, no patron to petition. The djinns — older than the state, beyond its jurisdiction — became the recipients of grievances no human office would hear. Taneja's careful argument is that this is a kind of justice-seeking, a quiet protest against bureaucratic erasure dressed up as devotion.

What you see if you go on a Thursday

Walk in past the ticket counter — entry is ₹25 for Indians — and head toward the back wall. Past the great pyramidal platform where the Ashokan pillar still stands. Through the arched chambers of the old mosque, where the floor is uneven and the smell of damp stone presses in. You'll see the candles before you see the people. Then the smoke. Then the letters.

People speak softly, if at all. Some weep. Many sit on the floor in groups, sharing food, reading prayers. Children run between them. A man unwraps a packet of sweets and presses it into a crack between two stones. A woman, holding three folded letters, walks slowly along the wall, reading each name aloud before tucking it in.

None of this is theatre. There is no guide explaining anything to anyone. It simply happens — every Thursday, at the foot of an emperor's fort, in a country where 70% of the population uses smartphones.

How to visit, respectfully

Firozshah Kotla is open every day except Mondays, 7am to 5pm. ASI ticket: ₹25 for Indians, ₹300 for foreign visitors. The grounds are large and you should plan for about 90 minutes if you want to walk all of it slowly.

If you go on a Thursday evening:

— Dress quietly. This is, for many people there, a place of prayer.
— Don't photograph people without asking. Photographing the walls and the letters is fine.
— Don't disturb the letters. They belong to whoever placed them there.
— Take off your shoes if you enter the mosque section.
— Bring water; there's no shade on the platform.

Most cities lose their dead. Delhi keeps them — in cracks, in walls, in Thursday afternoons. To walk through Firozshah Kotla on the right day is to encounter a 700-year-old fort that has become, against every plan of its builder, a working post office.