[simonh]

I don't think the Culture builds rings or spheres themselves, but they exist and they are aware of them. There are civilizations in the galaxy considerably more advanced than the Culture.

[dodobirdlord]

I believe the Culture is credited as having creating the ring in Consider Phlebas.

[mkl]

Do you mean Vavatch, that was scheduled for destruction? That was Culture, but an Orbital.

[arethuza]

Vavatch was destroyed by a militarised Culture GSV but it wasn't "owned" by the Culture.

[p_l]

Vavatch was, IIRC (I'd have to search through) built by Culture, but since then ceded, similarly the ships that helped evacuate it