The exit towards the North, overlooked by the tower from where Galileo observed Jupiter’s satellites.
According to old chronicles, the first walls of Padua were raised in 1195 and the first perimeter, the one enshrining the old Roman city centre, was completed in 1210. Others followed later, with the expansion of the city: two were added in the epoch of the Municipalities, at the times of Ezzelino, and at the times of the Carrarese. On the latter, in the 16th century Venice built the current walls.
The Molino door and bridge are some of the best-preserved remains of the first perimeter, which used to count 19 doors and passages; its name stems from the many water mills – 34 in 1300 AD – once floating on the river, which decreased to 24 in the 18th century and were finally abolished in the years 1883-1884.
The bridge, with five arches, has Roman origins and goes back to the years 40-30 BC, even if it was repeatedly rebuilt on site using original materials. Together with Pontecorvo, Molino Bridge is the only Roman bridge that is still in service.
The door of Molino Bridge has an ogival arch surmounted by a majestic tower. They say that from this tower Galileo saw the four satellites of Jupiter, as a stone dictated by the epigraphist from Padua Carlo Leoni (1812-1874): "da questa torre Galileo molta via de' cieli svelò".
From Porta Molino the Riviera dei Mugnai starts, where it is possible to see some sections of the medieval walls, partially included into modern buildings. In the district of Via Dante, where the old Roman street connected to the Porta, in the Middle Ages the craftsmen of leather and shoes used to work; the poorest ones, who could not afford a shop in the city, moved their business towards the Brenta Riviera, which today is extremely popular for the flourishing shoemaker business.
At the beginning of the 14th century the district around Ponte Molino (Mill Bridge) was a true industrial area: 34 massive mills were in action day and night. This was the largest concentration of mills at Padua, with roughly 50 more scattered along the city's internal waterways and in other parts of the territory. Millers had established in the Ponte Molino to take advantage of its powerful flow of water. These were 'floating' mills, built of wood on two or three hulls anchored in the river. The stone-walled mills built near water at Torricelle were naturally more stable and better suited to a variety of industrial applications, such as fulling wool, sawmilling and the typical grain milling. Still more mills were found at Ognissanti, Santa Maria in Vanzo and Prato della Valle. At the time of the commune, the mills belonged to the church, the commune itself, and to large land-owners. The miller rented the mill, paying with flour. The rule was that the miller would keep one cup of flour for every staio (roughly 2 litres) of grain milled. In the 1300s the mills became the property of the Carraresi signori. When the Venetians conquered the city they were confiscated and sold by auction. The millers' corporation was dedicated saints Rocco and Sebastian, and met at the altar in their name in the Church of St. Mary Carmine.