A squared trilogy is an ennealogy (series of 9) split into 3 trilogies, making it a trilogy of trilogies.
The 3 installments in each of the 3 smaller trilogies are normally direct sequels, but may in rare cases be prequels, parallels, etc (but never spin-offs). The one large trilogy is more flexible; It may be distant sequels, prequels, prequels, interquels, and others. It can still apply if there were single spin-offs or prequels etc added (which is likely), as long as they are outside of the 3 main trilogies.
- Jeff Smith's Bone is known more as an enneilogy, but it is split into 3 trilogies with slightly different themes; Vernal Equinox, Solstice, and Harvest
- Star Wars, now owned by Disney, has a third trilogy planned. It currently has 2 trilogies; the Original Trilogy, and the Prequel Trilogy.
- Sheri S. Tepper's True Game series is a trilogy of trilogies, each with a different protagonist.
- The Mega Man X series has a trilogy on each of 3 game consoles. A trilogy on the SNES (1-3), a trilogy on the PS1 (4-6), and a trilogy on the PS2 (7, 8, and Command Mission).
- The original Ultima series was a trilogy of trilogies, each of which was themed around a different motif: Age of Darkness (games one through three) were mainly straight-up hero-vs-villain plots; Age of Enlightenment (four through six) concerned your quest for the Avatarhood and spreading the Eight Virtues throughout Britannia; Age of Armageddon (seven through nine) centered on a new Big Bad who was actively corrupting the Virtues.