Actually an oval, this magnificent square is the vast main entrance into the Vatican. It's one of Bernini's most spectacular masterpieces, completed in 1667 after 11 years' work -- a relatively short time in those days, considering the vastness of the task -- and capable of holding 400,000 people. It's surrounded by a pair of quadruple colonnades, gloriously studded with more than 140 statues of saints and martyrs. Look for the two disks set into the piazza's pavement on either side of the central obelisk. If you stand on either disk, a trick of perspective makes the colonnades seem to consist of a single row of columns. Bernini had an even grander visual effect in mind when he designed the square. By opening up this immense, airy, and luminous space in a neighborhood of narrow, shadowy streets, he created a contrast that would surprise and impress anyone who emerged from the darkness into the light, in a characteristically Baroque metaphor. But in the 1930s, Mussolini ruined the effect. To celebrate the "conciliation" between the Vatican and the Italian government under the Lateran Treaty of 1929, he conceived of the Via della Conciliazione, the broad, rather soulless avenue that now forms the main approach to St. Peter's and gives the eye time to adjust to the enormous dimensions of the square and church, nullifying Bernini's grand conception.

The 85-foot-high Egyptian obelisk was brought to Rome by Caligula in AD 38 and was probably placed in his circus, believed to have been near here. It was moved to its current site in 1586 by Pope Sixtus V. According to legend, the monumental task of raising it almost ended in disaster when the ropes started to give way. In the absolute silence -- the spectators had been threatened with death if they made a sound -- a voice called out "Water on the ropes!" Strengthened by having water poured on them, the ropes held, and thus a Genoese sailor who dared to speak up had saved the day. He was rewarded with the papal promise that thereafter the palms used in St. Peter's Basilica on Palm Sunday should come from Bordighera, the sailor's hometown.

The emblem at the top of the obelisk is the Chigi star, placed here in honor of Alexander VII, a member of the powerful Chigi family who was pope when the piazza was built. Alexander had been categorical in dictating to Bernini his requirements for the design of the piazza. It had to make the pope visible to as many people as possible from the Benediction Loggia and from his Vatican apartments; it had to provide a covered passageway for papal processions; and it had to skirt the various existing buildings of the Vatican, while incorporating the obelisk and the fountain already there. (The fountain was moved to its current position, and a twin fountain was installed to balance it.)

Piazza San Pietro is the scene of large papal audiences as well as special commemorations, masses, and beatification ceremonies. When he's in Rome, the pope makes an appearance every Sunday around 11 AM (call the Vatican Information office to find out if the pope is in town and the exact time) at the window of the Vatican Palace. He addresses the crowd and blesses all present. The pope holds mass audiences on Wednesday morning about 10 (at 9 in the hotter months). Whether or not they are held in the square depends on the weather. There's an indoor audience hall adjacent to the basilica. While the pope is vacationing at Castel Gandolfo in the Castelli Romani hills outside Rome, he gives a talk and blessing from a balcony of the papal palace there. For admission to an audience (Prefettura della Casa Pontefice, 00120, Vatican City. 06/69883273. 06/69885863), apply for free tickets by mail or fax in advance, indicating the date you prefer, the language you speak, and the hotel in which you will stay. Or apply for tickets on the Monday or Tuesday before the Wednesday audience at the Prefettura della Casa Pontifice, open Monday and Tuesday 9-1, which you reach through the Portone di Bronzo (Bronze Door) at the end of the right-hand colonnade. You can also arrange to pick up free tickets on Tuesday from 5 to 6:45 at the Santa Susanna American Church (Via XX Settembre 15, near Termini. 06/42014554); call first. For a fee, travel agencies make arrangements that include transportation. Arrive early, as security is tight and the best places fill up fast.

On the south side of the square are the Centro Servizi Vaticani (Vatican Information Office. 06/69881662. Mon.-Sat. 8:30-7) and the Vatican Bookshop (Weekdays 8:30-7, Sat. 8:30-2). There are Vatican post offices (known for fast handling of outgoing mail) on both sides of St. Peter's Square and inside the Vatican Museums complex. You can also buy Vatican stamps and coins at the shop annexed to the information office. Although postage rates are the same at the Vatican as elsewhere in Italy, the stamps are not interchangeable, so any material stamped with Vatican stamps must be placed into a blue or yellow Posta Vaticana box. Public toilets are near the Information Office, under the colonnade opposite, and outside the exit of the crypt. Religious objects and souvenirs are sold at shops in the surrounding neighborhood.