We believe that at the end of her life on earth Mary was taken up into heaven. The early Christians treasured the bodies and tombs of the Apostles and the martyrs, and built churches over them. Yet no one every claimed to have the body of Mary or to be able to point to the place of her burial, because of the belief of Christians that her body was taken up to heaven.
Christians celebrated the feast of the "Going to Sleep of Mary" or the Dormition of Mary as far back as the fourth century. Later this feast was kept each year on 15th August and it was called the feast of the Assumption of the Blessed Virgin Mary.
In the ninth century it was such a big Christian feast day that King Alfred declared the 15th of August an annual public holiday. This is now the biggest annual feast of the Blessed Virgin Mary for Catholics everywhere.
In the year 1950 Pope Pius XII made a precise and infallible definition of it when he declared that all Catholics are to believe that at the end of her life Mary was taken up into heaven and reigns there with her Son as Queen of the angels and saints.
Mary shared in a unique way with her Son in the work of our Redemption. That is why we have always believed that as he rose from death and ascended into heaven so also she was lifted up both body and soul into heaven.