The Atiratra Agnicayana ( "the building up of the fireplace performed overnight") or Athirathram is the piling of the altar of Agni. It is a Srauta ritual of the Vedic religion and is considered to be the greatest ritual as per the Vedic ritual hierarchy. It has been claimed as the world's oldest surviving ritual. Its mantras are first attested in the Yajurveda Samhitas (Taittiriya, Kathaka; Vajasaneyi) of the Kuru Kingdom, c.1000 BCE, and its theological explanations are in the Brahmana texts. The practice of this ritual was generally discontinued among Brahmins by the late Vedic period, during the rise of Jainism and Buddhism in India. Nevertheless, a continuous, unbroken 3,000 year tradition has been claimed to exist among a few Nambudiri Brahmin families in Kerala, South India.

The Atiratra Agnicayana ( "the building up of the fireplace performed overnight") or Athirathram is the piling of the altar of Agni. It is a Srauta ritual of the Vedic religion and is considered to be the greatest ritual as per the Vedic ritual hierarchy. It has been claimed as the world's oldest surviving ritual. Its mantras are first attested in the Yajurveda Samhitas (Taittiriya, Kathaka; Vajasaneyi) of the Kuru Kingdom, c.1000 BCE, and its theological explanations are in the Brahmana texts. The practice of this ritual was generally discontinued among Brahmins by the late Vedic period, during the rise of Jainism and Buddhism in India. Nevertheless, a continuous, unbroken 3,000 year tradition has been claimed to exist among a few Nambudiri Brahmin families in Kerala, South India.