The city gate and walls at Largo Parlascio were built in 1157 as part of the 4th construction lot of the medieval city walls. Porta Parlascio takes its name from a place-name probably of Longobard origin that indicated the north east area of the city. It led straight to the main street that crossed the town from north to south and was connected to the road to Lucca via a bridge over the river Auser, flowing immediately outside the walls.

The size of the gate and the brackets carved with a pattern of foliage indicate the importance of this gate. It was the largest of all the city gates. In fact it was so large that it had to be made smaller shortly after completion, as can be seen from the brickwork still visible under the arch.

Porta Parlascio was a fortified gate with two stone towers on the outside to guard and defend. In 1995, archaeologists searching beneath the gate found the original street surfaced with pebbles and cobblestones.
After the first conquest of the city by Florence in the early 1400s, the medieval gate was reinforced with an outer gate designed by Filippo Brunelleschi. In 1543the medieval structure was converted into a bastion by the architect Nanni Unghero, with a five-sided rampart that is still standing. Entry via the gate was closed.

The bastion is at present derelict; during the second world war it was used as an air-raid shelter.