Yajna, the fire sacrifice, is the ritual at the heart of the Vedas and among the oldest continuously described rites in the world. A fire is consecrated in a precisely built altar, and offerings, clarified butter, grains, the pressed juice of the soma plant in the grandest rites, are made into it by trained priests reciting Vedic verses, the fire acting as the mouth of the gods and the carrier of the offering to them. The great public sacrifices could run for days and required a whole college of specialist priests, each responsible for a portion of the liturgy.
The Vedic worldview made yajna the mechanism that sustained cosmic order (rita): the sacrifice fed the gods, and the gods in turn upheld the seasons, the rains and the moral order. Later Hindu thought both interiorised the rite, reading the true sacrifice as breath, knowledge or self-offering, and largely displaced it with image-worship, yet the fire ritual never disappeared. Its portable domestic form, homa or havan, is performed to this day at weddings, house-blessings and other thresholds, keeping the Vedic fire alight within a very different religious world.