The Yasna is the central liturgy and it is performed by two priests in the consecrated area of a fire temple, with no congregation present — a fact that surprises people who assume liturgy implies an audience. It runs seventy-two chapters over roughly two hours and includes the pressing of haoma, an unidentified plant with the same name and function as the Vedic soma, in a metal mortar, its filtering and its consumption by the officiant. The Gathas are recited within it. The implements — the barsom bundle of metal rods, the mortar, the cups, the strainer — each have prescribed positions on the stone table. The point that matters historically is that this liturgy is why the Avesta survives: the texts were transmitted in priestly memory for a very long time because they had to be performed accurately, and the written Avestan script was devised comparatively late specifically to record the sound of a recitation. What was needed liturgically survived; what was not, largely did not.