The statues on the balustrade represent Christ the Redeemer (19 feet high), St. John the Baptist and 11 Apostles. St. Mathias is included because he is associated with the other "Eleven" in bearing witness to Christ's Resurrection

The Obelisk from Egypt was brought to Rome by Emperor Caligula in 37 AD. It originally stood in his circus on a spot to the south of the basilica, close to the present Sacristy.

Sixtus V had Domenico Fontana move it in 1586 to the center of St. Peter's Square

It is also a sun dial, its shadows mark noon over the signs of the zodiac in the white marble disks in the paving of the square. The obelisk rests upon four couchant lions, each with two bodies whose tails intertwine. http://saintpetersbasilica.org/Exterior/Facade/Facade.htm