VATICAN CITY-As the tomb of the first pope and the principal church of most of his 264 successors, St. Peter’s Basilica is Roman Catholicism’s greatest shrine. It’s also a treasure trove of artistic riches, with works by such artists as Michelangelo, Raphael and Bernini. At more than 600 feet long, with a dome 450 feet high, it is one of the biggest churches in the world. And with millions of visitors per year, it is one of the busiest tourist attractions anywhere. Keeping the mother church of Catholicism running-and tidy-is, not surprisingly, a monumental task. The job is entrusted to a corps of 75 men. Whether the job is reminding visitors to doff their baseball caps, or dusting a cornice 175 feet above the marble floor, it falls to one of the basilica’s “Sanpietrini.”