The Qutb complex holds the first congregational mosque built in northern India, begun in 1192 and raised with columns and carved stone taken from demolished temples, a fact its own foundation inscription states. In its courtyard stands a fourth or fifth century iron pillar, moved there from elsewhere, whose resistance to rust has been studied by metallurgists and whose Sanskrit inscription records the raising of a standard of Vishnu. The Jama Masjid, built under Shah Jahan in the 1650s, is the great mosque of Mughal Delhi and keeps a collection of relics attributed to the Prophet.
Sikh Delhi is written into the same streets. Gurdwara Sis Ganj in Chandni Chowk marks the place where Guru Tegh Bahadur was executed in 1675 after refusing to convert, having taken up the cause of Kashmiri Brahmins threatened with forced conversion, which is why Sikh tradition remembers him as a martyr for another community's freedom of religion. Rakab Ganj marks where his body was cremated, and Bangla Sahib stands where the eighth guru stayed during a smallpox epidemic and where water from its tank is taken as medicine.
The city has also been the site of communal killing within living memory. After the assassination of Indira Gandhi in 1984, several thousand Sikhs were murdered in Delhi over three days, and the commissions of inquiry into it ran for two decades. At the southern edge of the city the Bahai House of Worship, opened in 1986 and shaped as an opening lotus, holds no images and no sermons and is open to anyone who wishes to pray in it.