Every year around October and November, Hindus around the world celebrate Diwali, or Deepavali—a festival of lights that stretches back more than 2,500 years. Diwali 2020 occurs on Saturday, November 14. In India, the five-day celebration traditionally marks the biggest holiday of the year.

Like many Hindu festivals, there isn’t just one reason to celebrate the five-day holiday. Pankaj Jain, a professor of anthropology, philosophy, and religion at the University of North Texas, says that the ancient celebration is linked to multiple stories in religious texts, and it’s impossible to say which came first, or how long ago Diwali started.

Many of these stories are about the triumph of good over evil. In northern India, a common tale associated with Diwali is about King Rama, one of the incarnations of the god Vishnu. When an evil king in Lanka (which some people associate with Sri Lanka) captures Rama’s wife Sita, he “builds up an army of monkeys” to rescue her, Jain says.

The monkeys “build a bridge over from India to Sri Lanka, and they invade Sri Lanka and free Sita and kill that evil king,” he says. As Rama and Sita return to the north, “millions of lights are spread out across the city Ayodhya just to help them come back home, just to welcome them.” Lighting lamps has long been one of the ways that Hindus celebrate Diwali.

Diwali prayer candle, Pakistan

A Pakistani Hindu family offers prayers and light candles as they mark Diwali, the Festival of Lights, in Lahore, 2016.

Arif Ali/AFP/Getty Images

In the south, Diwali is popularly linked to a story about the Hindu god Krishna, a different incarnation of Vishnu, in which he frees some 16,000 women from another evil king. In the western state of Gujarat, the New Year coincides with Diwali (there are multiple New Years throughout India), and Diwali is associated with asking the goddess Lakshmi for prosperity in the coming year. During the festival, many celebrants exchange gifts and coins.

Other religions like Buddhism, Jainism, and Sikhism use Diwali to mark important events in their histories, too. Professor Jain says that while Diwali is a religious holiday, it’s also somewhat of a national holiday in India. Comparing it to Christmas in the United States, he points out that many non-Christians in America still buy a Christmas tree and give each other gifts.