Sigil Stones in The Elder Scrolls IV: Oblivion serve several important purposes:

• Closing Oblivion Gates: Each Sigil Stone is found at the top of a Sigil Keep inside an Oblivion Gate. When you pick up a Sigil Stone, it closes the gate and teleports you back to Cyrodiil. You get one Sigil Stone per gate closed

• Enchanting Items: Sigil Stones can be used to enchant weapons, armor, clothing, or jewelry without needing soul gems or an enchanting altar. Each stone has a unique magical effect that varies randomly and depends on your character level when you pick it up. The enchantment strength scales with your level, classified into Descendent (levels 1-4), Subjacent (5-8), Latent (9-12), Ascendent (13-16), and Transcendent (17+)

• Lore Significance: Lore-wise, Sigil Stones are quasi-crystalline artifacts inscribed with Daedric sigils that create liminal bridges-portals between Oblivion and the mortal world (Nirn). They are essential for opening and sustaining Oblivion Gates, as they enable Daedra Lords and mortals to pierce the dimensional barrier. They cannot be replaced by soul gems for this purpose

• Other Uses: Beyond gate creation and enchanting, Sigil Stones are used in rituals for summoning items and Daedra with the Atronach Forge and as power sources for Daedric siege machines. They can also create less permanent portals if bound to a location

In summary, Sigil Stones are key quest items that close Oblivion Gates and provide powerful, level-scaled enchantments for gear, while also holding deep lore significance as artifacts that bridge worlds