The Castello was first built by Galeazzo II. Visconte, in the latter half of the fourteenth century. Galeazzo’s stronghold incorporated one of the thirteenth century gates, the Porta Giovia—or, in Milanese, _Zobia_—which had kept the name of the corresponding gate in the Roman walls, named Giovia in honour of the Emperor Diocletian Jovius. It served at first solely for defence, and as a prison. Only a few years after its erection Galeazzo’s subtle son secured within its walls his first great prey—Bernabò Visconte, his uncle and fellow-sovereign. The fortress did not then extend beyond the city walls; these with the moat formed its defence towards the country. But Gian Galeazzo constructed a second citadel beyond the walls and moat, enlarging the enclosure to the dimensions which they occupy to-day—and enclosing Porta Giovia and a portion of the city walls in the new precincts. The Castello, so increased and strengthened, became the chief support of the tyrants of Milan. Its possession ensured dominion of the city. When Duke Giovanni Maria was murdered, the fortress was faithfully held against all attacks by Vincenzo Marliano for his lawful successor, Filippo Maria, who was able to enter through it into the seditious city at the head of an army and force the factions to accept his rule. This last of the Visconte sovereigns made his dwelling in the innermost keep of the Castle in gloomy seclusion, imprisoned by his own fears. His tyranny and dark habit of life invested the Castle with horror for his subjects, and immediately after his death they deliberately tore the great building down, stone by stone, at great cost. Only the foundations were left standing. But for a very brief time did the Milanese see the free sky unobstructed by menacing towers. On the overthrow of the Ambrosian republic and the accession of Francesco Sforza, the Castle began to be rebuilt, and before long the great fortress, enclosed within much stronger defences than before, was again in existence. It is this Sforza building, with the additions made by Francesco’s sons, which we see in the restored Castello of to-day, though the brave new battlements and towers give a poor idea of the substance of those walls which amazed King René of Anjou when he visited the works with the Duchess Bianca Maria in 1453, and of a building celebrated by many writers as the strongest and proudest in the world.