Langdon moves through the crowd in St. Mark’s Square, entranced by the architecture of the city and its unique sound, which is free from motor vehicles or sirens.

Behind him, Sienna spots Dr. Ferris lagging and catches him hiding in the crowd scrolling his “dead” phone. She realizes he is hiding something and that she must warn Langdon, but Dr. Ferris catches up to her first.

Langdon, speeding ahead, spots the famous Horses of Saint Mark on the façade of St. Mark’s Basilica, which remind him of the Venetian plundering of Constantinople in the Middle Ages, eliciting an epiphany.

The Horses of Saint Mark are not an original work of Venice but are in fact sculptures from antiquity that were looted from Constantinople early in their lives and moved about Europe during some of the continent’s many conflicts before returning at last to St. Mark’s Square.

Langdon remembers that the horses’ collars had been installed after their plundering to conceal the fact that the heads had been removed to facilitate their transportation to Venice from Constantinople. This fact fits Zobrist’s riddle poem.