**Answer by Matthew Bunson on 29-4-2006 (EWTN): **
The dogma of the Assumption – that Mary was taken up body and soul into heaven, after the completion of her earthly life (termed her dormition – or falling asleep in the Lord) – was proclaimed on November 1, 1950 by Pope Pius XII in Munificentessimus Deus; There was extensive acceptance and support for the doctrines among theologians and saints for centuries prior to their formal proclamation by a pope. The doctrines were subject to intense study over a period of centuries, requiring a long process before formal acceptance was granted.
We know very little about the exact date of the dormition and Assumption. It is possible, based on various writings, that the dormition occurred not too many years after Jesus’ death and Resurrection and took place either in Jerusalem or Ephesus. The earliest surviving reliable references to the Assumption are the sermons of St. Andrew of Crete, St. John Damascene, St. Modestus of Jerusalem and others. In the West, meanwhile, St. Gregory of Tours is generally credited with mentioning it first. St. John Damascene added that St. Juvenal, Bishop of Jerusalem, at the Council of Chalcedon (451), informed Emperor Marcian and Empress Pulcheria (who wished to possess the mortal remains of the Mother of God) that Mary died in the presence of all the Apostles, but that her tomb, when opened was found empty; the Apostles thus concluded that the body was taken up to heaven.
The doctrine was subsequently supported by a host of theologians, including Sts. Albertus Magnus, Thomas Aquinas, and St. Bonaventure. The doctrine was also promoted by such eminent later theologians as St. Bernardine of Siena, St. Peter Canisius, St. Francis de Sales, and St. Robert Bellarmine. Pope Benedict XIV (1740-1758) declared it a probable opinion.
The Feast of the Assumption was observed in Palestine during at least the 5th century, according to the life of St. Theodosius (d. 529). When it was celebrated in the Eastern Empire is a matter of some question, as it was divided between August 15 and January 18. Byzantine Emperor Maurice (d. 602) attempted to settle the date and chose August 15, according to the Liber Pontificalis, at least as far as the Eastern Empire was concerned.
In Rome, the oldest and only feast of the Blessed Virgin Mary was January 1, the octave of the birth of Our Lord. Thus before the seventh century no other feast was recognized, although there is some question concerning the feast found in the so-called Gelasian Sacramentary for August 15. That feast, however, did not mention the corporeal assumption of Mary. The Byzantine feasts for Mary, including the Assumption, were introduced in the pontificate of Pope Sergius I around 700, from where they found acceptance in other territories, including those in the West that actually kept the other Eastern date of January 18. By the end of the 8th century, the feast was universally recognized in the West on August 15. The octave was added in 847 by Pope Leo IV, and in 863, Pope Nicholas I made it equal to Christmas and Easter.
Father Frederick Jelly, O.P. approached the question of the dormition this way, in The Encyclopedia of Catholic Doctrine (by Our Sunday Visitor): “Although the dogma of the Assumption did not settle a number of questions regarding Mary’s departure from this life, the testimony of Tradition does seem to favor the theological opinions that she died and was most likely buried near the Garden of Gethsemane in Jerusalem, and that, in the likeness of her Son’s Resurrection, her body did not decompose after her death and burial but instead Mary was gloriously assumed intact.”