The large archway constitutes the only surviving part of the external façade of the Pusterla dei Fabbri, a secondary access that opened into the walls of Milan built starting from 1171. Originally located near the current Piazza Resistenza Partigiana, it is possible that the name of the monument derives from the metalworking workshops located nearby. The artifact consists of a round arch characterized by mighty marble ashlars concluded by an acute-angled ring, of simple and harmonious workmanship in the measures and in the interlocking system. On the two tax bases, the presence of tiny protomes should be noted: on the left, the relief of a bearded man with large wide eyes; on the right, that of a lion with open jaws. In 1902, after a heated debate in defense of on-site conservation, the monument was moved to Castello Sforzesco on the decision of the City Council. Since 1956, the Pusterla de Fabbri has been moved to Room I, where with its solemn grandeur it signals the start of the architectural and sculptural path of the Museum of Ancient Art.