Feroz Shah Kotla

Behind this grey wall lies what remains of Firozabad, the city founded in 1354 by Sultan Firoz Shah Tughlaq. Kotla means "citadel". Today it's a maze of broken arches, dark passages and a roofless mosque. It's also one of the most mysterious places in Delhi.

1A pillar no one could read

On top of a pyramid of arches stands a polished sandstone pillar about 13 metres tall. It was carved for the emperor Ashoka in the 3rd century BC and stood at Topra, in present-day Haryana. Firoz Shah had it brought here in 1356, wrapped in cotton and silk, on a 42-wheeled cart and then by boat down the Yamuna, according to his chronicler Shams-i Siraj Afif. No one at his court could understand the inscription. Its script, Brahmi, was only deciphered in 1837, by the Briton James Prinsep.

2Letters to the djinns

The most surprising thing happens on Thursdays. Since the late 1970s, according to the anthropologist Anand Vivek Taneja, hundreds of people come to these ruins to ask the djinns for help: the beings of "smokeless fire" mentioned in the Quran. They light candles and incense, offer milk and leave letters, sometimes photocopies with their photo and address, in the niches of the walls. They ask for a job, good health, a visa or a lost love to return.

Djinns exist in Muslim belief; that they live in these ruins and read their mail is popular tradition.

3What to look for

• Ashoka's pillar, gleaming on its pyramid.
• The soot stains left by candles in the niches.
• The arches of the mosque, where Timur prayed in 1398.