They are centrally located along the loggiato (exterior gallery), facing the Piazzetta, right in front of the Biblioteca Marciana; and they are pink, made with red marble from Verona, not white like the others.
Why is that?
It looks like the Doge made his appearance between the two columns when there were events and official ceremonies in St. Mark’s Square, like the Caccia ai Tori (Bull’s Hunt) or the Svolo del Turco (Flight of the Angel). During the Svolo del Turco for example, which took place during Carnival, an acrobat disguised as an angel descended from a rope from the bell tower to reach the two pink columns where the Doge waited for him.
But there’s a far more somber side to the story of these columns. It is said that, between them, death sentences were announced to the crowd standing below. If the culprit was an aristocrat, he was hanged right between the two columns and left there hanging for a few days as a warning to Venetians. (Pink was meant to symbolize the blood of the people sentenced to death.)
The gallows were placed right in front of the Clock Tower, so that the convict could see the exact time of his death.
It is also said that the convict had one last chance to be graced: on the loggiato, the fourth column from the corner is slightly out of alignment with the others; the convict who managed to walk around it without falling down would be saved. Apparently, very few succeeded.
So next time you’re in Venice, you may want to stop to see those two pink columns, picturing the Doge of Venice or the condemned as if you were a Venetian of times past observing the scene.