The central focus of all the churches and religious monuments on the site of St. Peter’s Basilica zero in on one man: St. Peter. And he was, to say the least, kind of a big deal. Per Britannica, Peter (who was originally known as Simon) was one of the original 12 apostles of Jesus Christ. Not only did Peter personally know Jesus from practically the beginning of the Messiah’s ministry, but he continued on after Jesus’ death as one of the growing religious movement’s most prominent figures. Prominence has its downsides, however.

Non-Biblical legend maintains that Peter spent his final years in Rome, where he got on the wrong side of the authorities and was martyred. As Romans were wont to do in many tales of martyrdom, they crucified Peter; but, upon his request to not show up Jesus, they flipped him upside down (via Columbia University).

The Vatican claims that a memorial beneath the basilica’s high altar was built long ago to mark the burial of St. Peter, now widely revered as the first pope. Tracing the history of the tomb and who may be in it gets complicated fast, however. Per Smithsonian Magazine, there are some bone fragments reputedly connected to the saint and which were excavated from beneath the basilica in the 1930s. Yet, there’s no scientific way of proving the connection. For many, it remains all a matter of faith.

Construction projects, even those sponsored by ultra-rich and well-connected popes, don’t come cheap. And even a single glance at the grandeur and opulence of St. Peter’s Basilica will tell you that some serious money had to go into building this place. That’s not so shocking, but the source of some of that money was perhaps so upsetting that it led some people to leave the church entirely.

According to a master’s thesis from Rollins College, a portion of the early funding for construction came from indulgences, one of the more controversial practices of the Catholic Church during this time period.

Per ThoughtCo, indulgences were effectively cash payments meant to reduce sin and time spent in purgatory. But many argued that this was nothing more than a cheat and that true salvation could only be achieved through either good works or whether or not God had already decided if you were heaven-bound (depending on who you asked). For Martin Luther and other emerging Protestants, the flagrant use of indulgences were enough to make them break away from the church. And it could well be that the dramatic structure of St. Peter’s Basilica represented such a moral thorn in many peoples’ sides that they could no longer align themselves with what they believed to be a morally and spiritually corrupt institution.

Known as the Vatican Necropolis, this burial complex dates back to the earliest church on site from the first-century era of Emperor Constantine. In the 1940s, Pope Pius XI, who wanted to be buried as close to St. Peter’s remains as he could, commissioned an archaeological investigation of the necropolis. According to Aleteia, tradition held that Peter was martyred around 64 A.D. and then interred in a pagan burial ground. The fourth-century Constantine, who was decidedly more accepting of Christianity, had a church built on the spot, with the altar of the basilica supposedly sitting right above Peter’s burial itself.

The investigation produced quite a few results, showing that many people had the same idea as Pius XI and had themselves buried nearby. A small box of bones, reportedly found with high-class purple cloth in a small niche, was uncovered during that first excavation. Yet Life reports that, in 1950, Pius XII said that we couldn’t be sure they were Peter’s and not the bones of one of the many buried in the necropolis. But his successor, Paul VI, turned around and said that the remains were probably the apostle’s.

But, if we can step away from the Peter controversy for a moment, the excavations have uncovered a rich history of both pagan and Christian burials in the Vatican Necropolis, some dating back more than a millennium. Some even boast impressive artworks, like intricate tile mosaics and elaborate carvings.

It’s obvious enough that there’s plenty to see within the walls of St. Peter’s Basilica and, of course, visitors can get a pretty nice view just by looking at the church’s monumental facade. But they should also turn 180 degrees and take in the view of the square just outside of the basilica. This piazza features a plethora of monumental columns, hundreds of saints’ statues, and an elaborate fountain.

As the University of Washington points out, there was always some sort of space in front of St. Peter’s Basilica. But the one tourists see nowadays is the product of a redesign by Baroque sculptor Gian Lorenzo Bernini in the 1650s. He produced a grand statement meant to reflect the basilica itself, as well as the message that the church welcomed the faithful with open arms and would shield visitors from the outside world. Bernini actually designed two sub-squares, the Piazza Obliqua (an oval-shaped space), and the more squared-off Piazza Retta.

There’s even an ancient Egyptian obelisk there, perhaps a little strange for what’s considered to be a Christian hub. PBS reports that it’s bare of any inscriptions, making its history rather mysterious. As legend has it, the obelisk was left standing despite its pagan past because it had been a witness to St. Peter’s martyrdom. Other tales, such as the one that claimed Julius Caesar’s remains were encased in a metal globe on the top, haven’t been definitively proven.

Perhaps because it’s one of the most famous artworks in the basilica, Michelangelo’s Pietà sculpture has been the focus of much attention over the years. And some of that scrutiny has resulted in some seriously bad press for this centuries-old masterpiece.

Michelangelo’s Pietà has been seriously damaged at least twice over the years, starting with an 18th-century incident. According to “Young Michelangelo,” the fingers on the Virgin Mary’s left hand were accidentally broken. They were subsequently restored by Giuseppe Lirioni in 1736, but now some wonder if Lirioni may have taken some artistic liberties and imparted his own take on the positioning of the fingers in question.

But the most shocking incident in the history of the Pietà happened right in front of numerous onlookers within St. Peter’s Basilica in 1972. That’s when Lazlo Toth, a Hungarian man, climbed over a barrier and dealt 12 punishing blows to the marble statue while proclaiming loudly that he was Jesus Christ. According to a report from the New York Times, the face, veil, and left arm of the Virgin Mary portion of the sculpture were badly damaged. According to Reuters, restorers painstakingly reconstructed the statue out of hundreds of fragments, using a combination of marble dust and special glue to make the joints practically invisible. Ten months after Toth’s attack, the statue went back on display, this time behind bulletproof glass.