Tradition olds that August 15 marks the oldest feast day of Mary—the Solmenity of her Assumption. Early Christians have been commemorating this belief as far back as the 4th century.
But it wasn't until November 1, 1950 that the celebration was officially established as a solemnity. On that day, Pope Pius XII proclaimed the Assumption a dogma of the Church, stating that at the end of her life Mary was taken up to heaven, body and soul.
While it may be an ancient tradition, its relevance continues to today. In 2011, Pope Benedict XVI explained that the Assumption helps Christians look to their future.
POPE BENEDICT XVI
August 16, 2011
It is a mystery of hope and joy for all of us. In Mary, one can see the goal of all of those who have joined their lives to Jesus.
His successor, Pope Francis, has made his devotion to the Virgin a central aspect of his papacy. And he has repeatedly emphasized Mary's assumption as something more than an old tradition.
August 16, 2020
It is of little use to go to the Moon, if we do not live as brothers and sisters on Earth. But that one of us dwells in the flesh in Heaven gives us hope: we understand that we are precious, destined to rise again. God will not let our body vanish into nothingness.
Thus, every year on August 15, the Catholic Church celebrates the Assumption as one of the 4 Marian dogmas.