What grand sacrifice did Yudhishthira perform after the war?

After the Kurukshetra War, Yudhishthira performed the Ashvamedha Yagna, or horse sacrifice.

The Ashvamedha was an ancient royal ritual designed to proclaim a ruler’s sovereignty. A consecrated horse was released to wander for a year. Any ruler who stopped or challenged it had to fight; rulers who allowed it to pass effectively acknowledged the sponsoring king’s supremacy.

In Yudhishthira’s ceremony, Arjuna followed the horse with an army and confronted rulers who resisted its progress. The ritual helped restore Yudhishthira’s authority after the devastating war and established him as the undisputed emperor of the realm. Krishna and Vyasa encouraged him to undertake it despite his grief and the kingdom’s depleted resources.

The event is narrated in the Ashvamedhika Parva, the fourteenth book of the Mahabharata. It is often confused with the Rajasuya, which Yudhishthira performed earlier, before the dice game and exile. The Rajasuya crowned his imperial ambitions; the Ashvamedha followed the war and reaffirmed his rule.