The Buddha's first sermon was preached in a deer park outside Varanasi, and the monument Ashoka raised there is now on every Indian banknote.
What happened here
Having become a Buddha, Gautama went to find the five ascetics who had abandoned him. What he taught them (the middle way, the four noble truths, the eightfold path), is called the first turning of the wheel of the teaching.
The significance is institutional as much as doctrinal. Before this there is an awakened man; after it there is a sangha, a community. Sarnath is where Buddhism becomes a religion rather than a private realisation.
The capital
Ashoka marked the site in the third century BCE with a stupa and a pillar. The pillar's capital (four lions back to back, above a frieze of four animals and four wheels, on an inverted lotus), was uncovered by F. O. Oertel in 1904.
Independent India adopted it as the State Emblem, and the wheel beneath it as the chakra on the national flag.
This is a genuinely odd outcome, and worth stating plainly: a Buddhist monument, from a country whose Buddhist population is well under one per cent, serves as the official emblem of a constitutionally secular and overwhelmingly Hindu republic. The choice was deliberate: Ashoka offered a model of Indian statehood that was ancient, indigenous, non-sectarian and associated with renunciation of conquest.
The capital itself is in the site museum. The column it stood on is broken and remains in place.
Destruction and recovery
The Dhamek Stupa still stands to thirty-nine metres. The Dharmarajika Stupa does not: it survives as foundations because a local landlord's workmen quarried it for building material in the eighteenth century, breaking into the relic chamber in the process.
The site was wrecked around 1194 during the Ghurid campaigns. Recent scholarship complicates the standard account by arguing that Brahmanical hostility contributed to the decline of Buddhist institutions here alongside the invasions, rather than invasion being a sufficient explanation on its own.
Alexander Cunningham excavated systematically in 1835-36.
Now
The Archaeological Survey holds the site, so it is a ticketed monument rather than a functioning temple. Thai, Tibetan, Japanese, Burmese and Sri Lankan temples have been built around the ruins, Theravada, Mahayana and Vajrayana communities all keeping a presence at a place none of them owns.