Djinns live in the heart of Delhi: they are spirits tending to the faithful seeking help. On Thursdays, they are busy when thousands turn up with letters for them.

Welcome to the ruins of Feroz Shah Kotla fort: it was built by Sultan Feroz Shah Tughlaq in the fourteenth century and now nestles between a cricket stadium and Delhi’s Ring Road. In the niches and alcoves of its stone walls, believers pray, light candles and diyas, and write letters to djinns, supernatural creatures of Islamic mythology made of fire rather than clay as humans are.