Audioguide by eArs

Hall of Rings

If you look around when you reach this room, you'll notice that the walls are covered with hundreds of diamond rings. That's why this space was known as the 'Diamond Room' in the mid-15th century. If you can't precisely distinguish them, it might help you to know that the rings are intertwined in groups of three, creating a knot called a 'triquetra', with the diamond having a pointy tip. This ancient symbol - certainly alluding to the Trinity - was also meant to suggest the perpetuity of a friendship or love. And even in the Middle Ages, diamonds were considered connected to these two noble sentiments. When set in a gold ring given by a friend, they had the power to ward demonic forces off from the wearer.
So it's not surprising that the Marquis of Ferrara, Nicolò III, granted this heraldic symbol to his most loyal collaborators, such as Uguccione Contrari. The colours chosen for the rings are not random either: indeed, green, white and red are the distinctive colours of the House of Este. As if that weren't enough, the friendship between the lords of Ferrara and the owners of the fortress is reaffirmed again in the vault. If you look up, you'll see the Contrari coat of arms at the intersection of the ribbing in the ceiling, surrounded by four floral medallions with the Este lion emblem that you already saw in the previous room.
Take a close look at the four felines... while three are depicted with their snouts from the side, seemingly walking according to the usual iconography, one is sitting and looking straight ahead. Dismissing the idea that it wants to devour us, in heraldry this is called a 'majestic lion', a symbol of royalty and wisdom. This is a unique example, as the Este lion has never been found depicted elsewhere with this particular heraldic attribute.