The Forces of Light and Dark in Ico
The Casket Chamber
In the tower at the rear of the fortress, just outside the throne room, is the casket chamber. Within, fifty two caskets which draw their power from sacrifices made over the course of generations line the walls. When they are activated they have the power to revive and change people. They use the power of Light Magic, and yet have some connection to Dark Magic.
The Chamber's Myriad Connections
The Casket Chamber ties into almost every aspect of the magic seen in Ico. It involves Yorda and the Queen, Ico and the boys like him, the Spirits, and Light and Dark Magic. Any coherent theory about what the Casket Chamber is and what exactly it does is thus going to rely on specific interpretations of all these other aspects of the game. While I will go into some of these individually in a separate section, for now I want to stay with the general truths that are part of them all. Examining this topic without pinning down all the others it is related to means that this section is going to be particularly vague and will not go into much detail. Even without attempting to determine the exact nature of the Casket Chamber, there are some aspects of it which will always prove interesting, and it is these I am going to examine now.
The Implications of The Chamber's Purpose
The first and I think most easily overlooked aspect of the Casket Chamber is the fact that it is designed to sacrifice people. Ico does open with the attempted sacrifice of Ico, and it is the survival of Ico and Yorda that is at stake as they attempt to leave the Fortress. However despite this, once it gets past the opening section the story focuses on the friendship and the struggles of the pair, and does not dwell on the possibility of their deaths. The mood of the story brightens considerably as they make their way through an imposing but not overtly threatening environment, helping each other toward their goal. The only remaining darker elements of the story take the more obvious form of the Queen and the Spirits, who are not seen constantly.
The Caskets & The Boys With Horns
The relationship between the Casket Chamber and the boys with horns tells us something extremely significant about the Spirits; that they are actually dead people. This, as with all things in Ico, is not told to us directly, but it is one of the most easily inferred aspects of the story. There are two points to consider to come to this conclusion: the Spirits seen in the Casket Chamber look just like Ico, and when each one is destroyed a corresponding Casket lights up. This tells us that each Spirit is linked to one of the caskets, and since they resemble the boys sacrificed in those caskets, each spirit is also linked to one of the boys. Furthermore, the purpose of the sacrifices was to activate the caskets, and they only activate after the Spirits are destroyed, suggesting that the destruction of the spirits is part of the sacrifice, which again suggests a link between the Spirits and the boys who were sacrificed.
Since it is fairly safe to assume that not everyone in Ico's world who dies becomes a spirit of this kind, we have to consider what it is that set the people who did become Spirits apart from 'normal' people. Since there are a large number of other Spirits in the fortress, it is unlikely (though possible) that being sacrificed in the Casket Chamber is the common thread, especially since the spirits are apparently destroyed as part of the process. We can look it at from the opposite perspective though. It is actually possible that the 'difference' that causes people to become Spirits is the very thing which makes them suitable for sacrifice in the Casket Chamber. This would explain why destroying the Spirits is a part of the process of activating the Casket Chamber; because the people who are required for the sacrifice become (or leave behind) Spirits when they die, they are not fully 'dead' until the Spirit is destroyed. This 'difference' is likely the same one which causes them to be born with horns.
The boys with horns held significance for the Fortress before they were used as sacrifices by the Queen. The Idol Doors throughout the Fortress contain images of the boys. While it is suggested that among Ico's people the inheritance of the horns is quite uncommon, it is possible they were more common at some point in the past. Outside the Tower which houses the Casket Chamber there is a statue of a man with horns, looking in toward the Tower, like an eternal guard. Some of the Spirits also bear a resemblance to adult versions of the sacrificed boys. Again, without much speculation very little beyond this can be told, however it does let us know that the people with horns were around when the Fortress was populated, were important to it somehow and, given that the boys in the Idol Doors are in the same pose as Yorda was in her cage, were probably not the better for it.
The Caskets' Powers
We only have one of example of the Casket Chamber being activated, so it may have a greater overall purpose of which we will remain unaware. However, even this single demonstration of its power is extremely significant, as it appears to bring back the dead. The Queen uses it to bring Yorda back after killing her on the bridge. Her reason for doing this is presumably because it brings her back as a Spirit, the idea being that the Queen would take over this new Dark Magic body. This gives us further insight into Light Magic, and into the relationship between Light Magic and Dark Magic.
The Casket Chamber's power manifests in the same way as Yorda's, and the other examples of Light Magic seen throughout the story. In every other instance it seems simply to be a transfer of magical energy, either activating some kind of device or destroying a Spirit, as opposed to a more complex magical power like the portals the Spirits appear from. However, the chamber's power actually does something, rather than simply activating something else, and on top of this it results in the creation of a Dark Being. Thus, while it manifests in the same way, it is obviously actually quite a different power than the others we see.