On this day in 1531, Our Lady of Guadalupe appeared to an Indian named Juan Diego (whose feast is today).

At the time of Mary’s appearance, Catholicism was relatively new in Mexico. It is thought that the first Catholic Mass on Mexican soil had occurred less than 15 years earlier. The Catholic Encyclopedia notes that Mary’s apparition would have “a powerful effect, the increase in conversions being very noticeable after that time.”

Today Catholicism remains the majority religion in Mexico. The 2010 census found that about 84 percent of respondents identified themselves as Catholic; the Vatican estimates the number is higher (nearly 92 percent).

But, as in many countries, the number of Catholics leaving the Church has increased in recent years. According to one study, more than 1000 Mexicans left the Catholic Church everyday over the last decade. One Mexican bishop estimated that of people remaining in the Church, only 10 to 20 percent go to Mass and are involved in their parish.

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The Archdiocese of Mexico City is the world’s largest Catholic archdiocese with approximately seven million Catholics. It has about 150,000 baptisms a year – a figure that is more than the entire Catholic population in many dioceses around the world.