Explore the Commissioning of this artwork.
The sculpture has a long history, beginning in 1654, when Bernini began the work, quite possibly commissioned by Pope Innocent X.
 The original plan was to place the sculpture within St Peter's Basilica. However, when Alexander VII assumed  the papal throne a year later, the  project was reinvigorated, securing the arrival of a large block of marble which Bernini could use to put existing drawings and sketches into practice. However, for reasons that are unclear, the project was delayed again, and Bernini did not start work on the block until 1662.
It was only at an undefined point in the 1660s that the location for the statue become the new Scala Regia that Bernini himself was designing. Bernini continued refining the equestrian sculpture, and changes were made to the design to cope with the new location on the Scala Regia. Huge clay models of the sculpture were placed within the niche, giving Bernini an idea of what the final composition would look like when placed in situ. Because of the tallness of the niche, overwhelming the sculpture, folding, dynamic drapery was added to the overall decorative effect, to be placed behind the marble horse. 
This allowed Bernini to make the final touches to Constantine, and it was declared ready at the end of 1668
Transporting the sculpture from Bernini's studio to Scala Regia took ten days and required guards to look after it during the night. A variety of straw, winches, planks and beams, plus sledges and oxen were needed to pull the massive sculpture. It finally arrived on 12 January 1669. Architectural and decorative work (such as the drapery) on the niche around the sculpture continued through 1669, as did polishing of the statue itself.
Scala Regia