The story goes like this, the apostle James was in Spain preaching the Gospel and things weren't going well. Mary appeared to him (on top of a pillar) to encourage him in his endeavors. Of course, Spain was eventually converted and the Spaniards continue to honor St. James. In a weird twist, according to most chronologies, Mary was still alive when she appeared to James - meaning that she could bilocate. Mary, as Our Lady of the Pillar, is venerated in Spain and many parts of Latin America.
For us Marianists, this is a big day, too. On October 11, 1797 (the day before the feast), Marianist Founder Blessed William Joseph Chaminade arrived in Zaragoza. He had just been exiled from his native France because of the ongoing persecutions of the French Revolution. He would spend the next three years in Zaragoza, spending a great deal of time praying before the Shrine of Our Lady of the Pillar. And during those three years, something happened. Yes, something, because we don't really know what happened. Fr. Chaminade wrote practically nothing about his time in Spain, and only mentioned it in passing. However, he received some sort of inspiration or mission before Our Lady of the Pillar to return to France and "re-Christianize" the country devastated by the Revolution.