The gate is marked by a landmark triumphal arch called Arco della Pace, dating back to the 19th century, although its origins can be traced back to a gate of the Roman walls of Milan. A gate that roughly corresponds to modern Porta Sempione was already part of Roman walls of Milan. It was called "Jupiter's Gate". At the time, the gate was meant to control an important road leading to what is now Castelseprio. Very little remains of the original Roman structure; some Roman tombstones that used to be placed by the outer side of the walls have been employed in the construction of later buildings such as the Basilica of Saint Simplician.