The earliest known written reference to the Assumption can be found in the Greek text De Obitu S. Dominae, which dates to the fourth or fifth century but has been attributed to St. John himself. In the East, it is mentioned in the sermons of St. Andrew of Crete, St. John Damascene, St. Modestus of Jerusalem and others.
In 451 AD, at the Council of Chalcedon, the Emperor Marcian and Pulcheria desired to own the body of Mary, the Mother of God. St. John of Damascus tells us that St. Juvenal, Bishop of Jerusalem, told them that, "Mary died in the presence of all the Apostles, but that her tomb, when opened, upon the request of St. Thomas, was found empty; wherefrom the Apostles concluded that the body was taken up to heaven." The Catholic Church does not, however, claim to derive this doctrine from any of these early writers, but from Apostolic Tradition itself, which these early sources merely point to.
The Assumption of Mary has also been celebrated since early times with a Feast day. We do not know exactly where or when this celebration first occurred, but according to the life of St. Theodosius (d. 529) it was celebrated in Palestine before the year 500, probably in August. It has been celebrated at other times of the year in various places, however, such as in Egypt and Arabia, where it was observed in January. By 700 it was one of the principle feasts in Rome, and was a Holy Day of Obligation. As we do not know exactly where or when Mary died, we cannot mark the exact anniversary of her death, but we can still remember her Assumption with this celebration.
Many will argue that nowhere in the Bible can mention be found of Mary's Assumption. In Genesis, Enoch is said to have been assumed, and the same goes for Elijah in 2 Kings. So if Mary was truly assumed, then wouldn't this event have warranted mention in the Bible? On the face of it, this argument seems to hold weight. There are no express Scriptural proofs that show the validity of this doctrine. As Catholics, though, we need not rely solely on the Bible as our rule of faith. For us, it is enough that the living, infallible, teaching Church has told us that it is true, and it must be so. This requires an examination of the Protestant doctrine of sola scriptura (Scripture Alone), and will be dealt with later. For now it is important to point out that nowhere in the Bible does it exclude the possibility of the Assumption. In fact, in Matthew 27 it describes a scene where "graves were opened, and many bodies rose out of them, bodies of holy men gone to their rest: who, after his rising again, left their graves and went into the holy city. . ." This scene certainly seems to imply that such a thing as the Assumption is possible.
If one were to look to the Scripture for references to Mary's Assumption, the best place to look is the Book of Revelation, chapter 12. "And a great portent appeared in heaven, a woman clothed with the sun, with the moon under her feet, and on her head a crown of twelve stars; she was with child and she cried out in her pangs of birth, in anguish for delivery. And another portent appeared in heaven; behold, a great red dragon, with seven heads and ten horns, and seven diadems upon his heads. His tail swept down a third of the stars of heaven, and cast them to the earth. And the dragon stood before the woman who was about to bear a child, that he might devour her child when she brought it forth; she brought forth a male child, one who is to rule all the nations with a rod of iron, but her child was caught up to God and to his throne, . . ." This reading, of course, requires the reader to look for a deeper meaning than that normally given by commentators. The woman, to them, refers to some collective entity, such as the Church. However, since the dragon is always identified with Satan, and the child always Christ, and these are both singular entities, it makes sense that the woman should be identified first as a singular entity, and secondarily as a collective entity. The singular entity is, of course, Mary. John's vision of Mary in heaven with her son, Jesus, only makes sense if she had been Assumed into heaven, as Pope John Paul II as well as Pius X have stated. And this is, of course, what the Apostles believed happened, according to what the Bishop of Jerusalem said at the Council of Chalcedon, as we read above.
In fact, the absence of a body, or any remains at all, attributed to Mary speaks volumes. The Biblical silence on her assumption is neither an affirmation or a rejection of the fact--it is simply silence. But the silence of anyone claiming to have, or have seen, her earthy remains is worth noting. From the very beginning of the Church, Catholics have had a special veneration for the saints. The bones of the martyrs killed in the Coliseum were gathered up and preserved almost immediately, according to the biographies of those first Christian victims. Cities would vie for the claim to fame of being the final resting place of a famous saint. For some of the more famous saints, the bones were even divided up so that more than one town could claim them. These relics were preserved and venerated and were objects of great devotion. Surely a saint such as Mary, the most well known of all, who had such a special honor among all the saints, would be preserved and venerated more than any other. Yet no city anywhere has ever claimed her remains. We know she lived for a while in Ephesus with John and may have died there. There is also a good case that she may have died at Jerusalem and her temporary tomb is said to be there. Yet neither of these cities claims or ever has claimed to have her corporeal remains. Nowhere are her bones venerated. No one claims to have them. Why not? Because there were no remains to venerate and the people of the time knew it.
Mary's Assumption cannot be explained without also considering the doctrine of her Immaculate Conception. I cannot give that doctrine a full treatment here, but it states that Mary was conceived immaculately, without the stain of original sin. That from her conception she was set aside, chosen by God, to be the New Eve, the one to bear Christ to the World. Death and decay are the punishments for original sin, and since Mary was free from this stain, she was free of its consequences. So why did she die? If she died, it was because she was united with Christ. It was her desire to do the will of God, and just as Christ chose to die for our sins so that we may be redeemed, she chose to suffer and die an earthly death to be united with her son. Just as we all will one day be reunited with our physical bodies in our eternal home, Mary's body was taken into Heaven along with her soul. God would not allow her body, the body of His servant, free of sin, to corrupt. Her assumption gives us a glimpse of what the final destination of all of us may be.