The Assumption is the oldest feast of Our Lady:
"For a time, the ‘Memory of Mary’ was marked only in Palestine, but then it was extended by the emperor to all the churches of the East. In the seventh century, it began to be celebrated in Rome under the title of the ‘Falling Asleep’ (Dormitio) of the Mother of God.
"Soon the name was changed to the ‘Assumption of Mary,’ since there was more to the feast than her dying. It also proclaimed that she had been taken up, body and soul, into heaven."
'Come, let us worship the King of kings, for today his Virgin Mother was taken up to heaven.'
[The Assumption was infallibly defined by the pope in 1950. In this sermon, Monsignor Knox referred to the action as "a gesture against materialism."
It was a century earlier that the Church dogmatically stated Mary's Immaculate Conception -- that from the first moment of life in Anna's womb, she "was never subject to original sin."]