Emperor Constantine, the first Christian emperor of Rome, ordered to build a basilica on Vatican Hill. The location was symbolic: this was the place where Saint Peter, the chief apostle, was buried in 64 A.D. A small shrine already existed on the site but it was now replaced by a new building church was completed around 349 A.D. In the middle of the 15th century, the basilica was falling into ruin and pope Nicolas V ordered the restoration and enlargement of the church after plans by Bernardo Rossellino. After Nicolas V died, works were halted. In 1506 pope Julius II laid the first stone of a new basilica which was to become the largest in the world.
Julius II appointed Donato Bramante as the chief architect of the new Basilica. In 1547 Michelangelo succeeded Bramante. He designed the imposing dome and altered some of the original plans. Michelangelo died in 1624, two years before the completion of the dome. The St. Peter's basilica was dedicated by pope Urban VIII in 1626. Ever since, this church has been the center of Christianity, drawing pilgrims from all over the world. The building itself is truly impressive. The largest church in the world, it has a 218 meter long nave. The basilica's dome, designed by Michelangelo is the largest dome in the world measuring 42m in diameter and reaching 138 meter high (more than 450ft). The interior, which includes 45 altars, is decorated by many famous artists. Some of the most important works in the church are the Pietà by Michelangelo, the papal altar by Bernini, the Throne of St. Peter - also by Bernini - and the Monument to the Stuarts by Canova.
The opulent interior can be visited daily for free although a strict dress code is enforced. You can also visit the dome itself (entrance is not free, but it's worth it). You have the option of taking the elevator or the stairs, the latter being a bit cheaper. The elevator brings you to the bottom of the dome from where a small, long and mostly spiral staircase brings you to the top of the dome. From there you have a magnificent view of Rome and of the Saint Peter's square in particular. The famous square with long symmetrical colonnades was designed by Bernini. It features a central obelisk and two identical fountains. Near the entrance of the Basilica you will probably encounter some of the famous Swiss guards. Since 1506 when pope Julius II invited Helvetian soldiers to join the small Vatican army, they have been the guards of the Vatican and the pope in particular. All entrants to the army must be Swiss, catholic and they must take the oath of loyalty to the pope. This oath is taken May 26th, to commemorate the sacking of Rome on the same day in 1527 when Swiss guards protected pope Clement VII during his escape to the Castel Sant'Angelo. Of the 189 guards, only 42 survived.
St. Peter's is located in Vatican state, across the river Tiber, west of Rome's center. Vatican State is completely surrounded by the city of Rome.