Inside the basilica, artists decorated the walls, ceilings, and columns. Marble, gilt (a thin layer of gold), and mosaic (tiny pieces of colored stone laid in patterns) cover the interior Basilica. The walls are lined with enormous sculptures of Catholic saints and popes. A marble staircase leads to the underground tomb of Saint Peter.
An altar stands directly beneath the dome and above the tomb. Around the altar is a bronze structure called the Baldacchino. It was built by the artist Gianlorenzo Bernini (1598–1680). The Baldacchino is 98 feet (30 m) tall. Its four columns are twisted and carved to look like the stems and leaves of plants.