A:Do you know when the apparitions started? The earliest I've heard of, that the Vatican looks favorably on, is 1531 in Mexico.
St. Catherine of Siena had apparitions in the Fourteenth Century that are fully accepted.
http://www.apparitions.org/
Apparitions have been known from the earliest of Christian times. St. Augustine (400 AD) classified them into categories: corporal, imaginative, and intellectual visions. The book of Revelation was written under a state of ecstasy. As to the first reported apparition of Mary:
"The earliest recorded Marian apparition was in AD 352 to an elderly couple in Rome. The story goes like this: On a hot August night, Mary appeared requesting a shrine to be built on one of the city's celebrated hills. The following morning, the city awoke to find snow covering the Esquiline Hill. Hence, St. Mary Major, "Church of St. Mary of the Snow" can be found on this hill today. This church is considered to be one of the largest and most important churches dedicated to the Blessed Mother in the Western Church. Since this initial apparition, the number of reported ones has only grown."
As to the Church Fathers, St. Gregory of Nyssa recorded an appearance by the Blessed Mother to St. Gregory Thaumaturgis and St. Ambrose reported a visit while in prayer in the midst of his struggle with the Arian heresy.
God continues to work through Mary and His saints to bring us to Him. Apparitions are one way of giving messages or comfort to the Church under persecution or difficulty.
Regards
The earliest known is to St. James the Great in AD 39, then to Pope Liberius (352), then to Richeldis de Faverche (1061), then to St. Dominic, instituting the Rosary prayer in 1214, then to Saint Simon Stock, instituting the Brown Scapular, in 1251.
Of especial importance to the Americans is the apparition to Juan Diego, 1531, in Villa Guadalupe.