Situated near to the Porta Palazzo district, the imposing Porta Principalis Sinistra gives access from the north to the Quadrilatero. Its structure, with a small archaeological park beside it, is a double arched gateway with a courtyard facing the city, and two corner towers more than 30 metres high. Don't be fooled by the statue of Julius Caesar – it has only been there for less than a century!

After the fall of the Roman Empire, the Palatine Gate retained its function as a fortified palalce along the road to the cities now known as Pavia and Milan. However, the building has been heavily altered over the centuries. The left-hand tower was rebuilt in the 15th century, while in the 18th century the building was used as a prison. Extensive restoration work was carried out in the 20th century, when cars still passed beneath the arches. However, it is possible that the name in use is really quite ancient, and depended on the Gate's proximity to the palace of the Lombard rulers.