It is one of the oldest surviving gates of the city, dates back to 1285, the year in which started the sixth circle of walls. Like the other city gates was lowered in 1526, to be less vulnerable to the attacks of the new artillery, and was covered by the loggia with sloping roof, on top of which it is a sign metal weathervane. The Port takes its name from the before square called "Il Prato", that branches off the road leading to the city of Prato. In ancient times, this area was allocated to market cattle weekly. Until a few years ago, on the inner bezel there was a fresco depicting a Madonna and Child with Saints, attributed to Michele di Ridolfo, today moved to restoration.