 There is some evidence that suggest that already by the 6th century, "hērbad"s performed advanced theological tasks, including translations and interpretation of Avestan texts.The 10th century "Denkard" refers to the high-priest Tansar, who, in legend, is attributed with the collation of the Avesta, as "hērbad".Following the collapse of the Sassanid state in the 6th century, after which Zoroastrianism began to be supplanted by Islam, the increasingly impoverished Zoroastrian communities found it difficult to support a priesthood known only for their scholarship.