And so it goes. A woman clad all in white, who estimates her age at 80, or possibly 90, visits every Thursday to petition for improvements in her “three nasty daughters-in-law.” A snub-nosed tailor from Old Delhi visits when he is racking his brain, unable to complete an especially difficult dress, and wondering why he calls himself a tailor at all.

“When I go home, I find that I can make the dress,” he said happily. “That happens because of the djinn.”

Delhi has been reinvented so many times by so many powers that it can be difficult to know where its heart is — in the edifices left behind by the British or the austere medieval tombs of the Mughals. By comparison, there is nothing so extraordinary about the ruins of the castle, built by the sultan Firoz Shah Tughlaq, now squeezed between a cricket stadium and the Ring Road, except that they have survived the metastasis of the city for 700 years.

But if you sit long enough on a Thursday, you can see the past in living people. Anand Vivek Taneja, an anthropologist at Vanderbilt University who is writing a book about djinn veneration here, traces the letter-writing tradition to a form of governance that was common in 14th-century Delhi, when royal guards were removed and subjects were allowed to enter the palace to directly petition the Tughlaq sultan.