Built in the 2nd century as a means to cross the Tiber from Rome to the Mausoleum of Hadrian, the Pons Aelius or Aelian bridge is now known as the Ponte Sant’ Angelo. This undoubtedly is the most beautiful bridge to cross the Tiber and is on the main tourist route, primarily to get to Castel Sant’ Angelo, but also for the purpose of seeing the statuary .
During the Baroque period, Pope Clement IX commissioned Bernini to design 10 statues that represented the elements of the Passion of Christ to adorn the bridge that also served as the main thoroughfare to the Vatican . Bernini himself, only completed two of the statues including the angel holding the crown of thorns. The statue on the left is holding the spear that pierced Christ’s side, while the one on the right holds the cross, the most obvious image to represent Christ’s Passion.
If you look closely at the hand of this statue to the right in this photo, you will see it holding nails, or spikes.
The statue of the angel on the left is holding the flagrum or whip for the flagellation or scourging of Christ, while the one on the right is a copy of the Bernini statue that depicts an angel holding the crown of thorns. The original Bernini now resides in the church of Sant’ Andrea delle Fratte.
For more historical information: http://en.wikipedia.org/wiki/Ponte_Sant'Angelo