On Saturday, December 9, 1531, a neophyte Catholic named Juan Diego was hurrying down Tepeyac hill in Guadalupe Hidalgo to hear Mass in Mexico City, and the Blessed Virgin appeared and sent him to Bishop Zumárraga to have a church built where she stood. She was at the same place that evening and Sunday evening awaiting the bishop’s answer. The bishop asked Juan Diego to ask a sign of the lady who said she was the mother of the true God. Juan Diego agreed readily, and the bishop left the sign to the apparition. However, Juan was occupied all Monday with an uncle who seemed dying of fever, so at daybreak on Tuesday, December 12, the grieved nephew was running to the St. James’s convent for a priest. As he went along, the Blessed Virgin came to meet him and said: “What road is this thou takest son?” Reassuring Juan about his uncle whom at that instant she cured, she called herself Holy Mary of Guadalupe she told him to go again to the bishop. Without hesitating he joyously asked for the sign. She told him to go up to the rocks and gather roses. He knew it was neither the time nor the place for roses, but he went and found them. Gathering many into the lap of his tilma (a long cloak made of maguey cactus fiber used by Mexican Indians) he came back. The Blessed Mother, rearranging the roses, bade him keep them untouched and unseen till he reached the bishop. Entering into the presence of Bishop Zumárraga, Juan offered the sign. As he unfolded his cloak the roses fell out, and he was startled to see the bishop and his attendants kneeling before him: the life size figure of the Virgin Mother, just as he had described her, was glowing on the poor tilma. A great mural decoration in the renovated basilica commemorates the scene. The picture was venerated, guarded in the bishop’s chapel, and soon after carried processionally to the preliminary shrine. Although nearly 500 years old, the tilma has been miraculously preserved and can be seen today.
The clergy, secular and regular, has been remarkably faithful to the devotion towards Our Lady of Guadalupe, the bishops especially fostering it. Popes Benedict XIV was a strong supporter, and decreed that Our Lady of Guadalupe should be the national patron, and made December 12th her Feast Day. Juan Diego was canonized on July 31, 2002 by Blessed Pope John Paul II in Mexico City.
(Summarized from the Catholic Encyclopedia)