The Basilica di San Pietro, or simply St. Peter’s, is the holiest shrine of the Catholic Church, built on the site of St. Peter’s tomb by the greatest Italian artists of the 16th and 17th centuries. One of the lines on the right side of the piazza funnels you into the basilica, while the other two lead to the underground grottoes or the dome. Whichever you opt for first, you must be properly dressed—a rule that is very strictly enforced.

In Roman times, the Circus of Nero, where St. Peter is said to have been crucified, was slightly to the left of where the basilica is now located. Peter was allegedly buried here in a.d. 64 near the site of his execution, and in a.d. 324, Emperor Constantine commissioned a church to be built over Peter’s tomb. That structure stood for more than 1,000 years, until it verged on collapse. The present basilica, mostly completed in the 1500s and 1600s, is predominantly High Renaissance and baroque. Inside, the massive scale is almost too much to absorb, showcasing some of Italy’s greatest artists: Bramante, Raphael, Michelangelo, and Maderno. In a church of such grandeur—overwhelming in its detail of gilt, marble, and mosaic—you can’t expect much subtlety. It is meant to be overpowering.

Going straight into the basilica, the first thing you see on the right side of the nave, the longest in the world, as clearly marked on the pavement, along with other cathedral measurements (in the first chapel) is Michelangelo’s graceful “Pietà,” one of Rome’s greatest treasures, created in the 1490s when the master was still in his 20s but clearly showing his genius for capturing the human form. (The sculpture has been kept behind reinforced glass since an act of vandalism in the 1970s.) Note the lifelike folds of Mary’s robes and her youthful features; although she would’ve been middle-aged at the time of the Crucifixion, Michelangelo portrayed her as a young woman to convey her purity.

Further inside, Michelangelo’s dome is a mesmerizing space, rising high above the supposed site of St. Peter’s tomb. With a diameter of 41.5m (136 ft.) it is Rome’s largest, supported by four bulky piers, decorated with reliefs depicting the basilica’s key holy relics: St. Veronica’s handkerchief (used to wipe the face of Christ); the lance of St. Longinus, which pierced Christ’s side; and a piece of the True Cross.

Under the dome is the twisty-columned baldacchino, by Bernini, resting over the papal altar. The 29m-high (96-ft.) ornate canopy was created in part, so it is said, from bronze stripped from the Pantheon. Bernini sculpted the face of a woman on the bases of each of the pillars; starting with the face on the left pillar (with your back to the entrance), circle the entire altar to see the progress of expressions from the agony of childbirth through to the fourth pillar, where the woman’s face is replaced with that of her newborn baby.

Just before you reach the dome, on the right, the devout stop to kiss the foot of the 13th-century bronze of St. Peter, attributed to Arnolfo di Cambio. Elsewhere the church is decorated by more of Bernini’s lavish sculptures, including his monument to Pope Alexander VII in the south transept, its winged skeleton writhing under the heavy marble drapes.

An entrance off the nave leads to the Sacristy and beyond to the Historical Museum (Museo Storico), or treasury, which is crammed with richly jeweled chalices, reliquaries, and copes, as well as the late-15th-century bronze tomb of Pope Sixtus IV by Pollaiuolo.

You can also head downstairs to the Vatican grottoes, with their tombs of the popes, both ancient and modern (Pope John XXIII got the most adulation until the interment of Pope John Paul II in 2005). Behind a wall of glass is what is assumed to be the tomb of St. Peter.

Visits to the Necropolis Vaticana and St. Peter’s tomb itself are restricted to 250 persons per day on guided tours (90 min.). You must send a fax or e-mail 3 weeks beforehand, or apply in advance in person at the Ufficio Scavi (tel. 06-69873017; e-mail: scavi@fsp.va; Mon–Fri 9am–6pm, Sat 9am–5pm), which is located through the arch to the left of the stairs up the basilica. For details, check www.vatican.va. Children 14 and under are not admitted to the Necropolis.

After you leave the grottoes, you find yourself in a courtyard and ticket line for the grandest sight in the basilica: the climb to Michelangelo’s dome, about 114m (375 ft.) high. You can walk all the way up or take the elevator as far as it goes. The elevator saves you 171 steps, and you still have 320 to go after getting off. After you’ve made it to the top, you’ll have a scintillating view over the rooftops of Rome and even the Vatican Gardens and papal apartments.

A St. Peter’s Warning

St. Peter’s has a hard-and-fast dress code that makes no exceptions: Men and women in shorts, above-the-knee skirts, or bare shoulders are not admitted to the basilica, period, and hats should be off. I’ve occasionally seen guards handing out disposable cloaks for the scantily clad, but don’t count on that: Cover up or bring a shawl. The same holds for the Roman Necropolis and the Vatican Museums.

An Unofficial Assist

Though it’s not an official portal for Vatican City, the independent website www.stpetersbasilica.info offers a wealth of current, detailed, and helpful information for navigating your way through St. Peter’s and its associated components.