Throughout the game, most players saw the Ancients as a primitive race only concerned with cultivating the earth. Surprisingly, this conception may be wrong. While the Ancients did indeed live a simple life, it's suggested they also held technology beyond that of the present Shinra Corporation. In particular, evidence has been found to suggest they actually travelled in space.
...During Cloud's flashback of Nibelheim, Sephiroth discovers his 'heritage' and hisses towards Cloud,
"This Planet originally belonged to the Cetra. Cetra was an itinerant race. They would migrate in, settle the Planet, then move on...
"At the end of their harsh, hard journey, they would find the Promised Land and supreme happiness."
Pay particular attention to the phrase "They would migrate in, settle the Planet, then move on..." This sentence is rather ambiguous in meaning. Sephiroth was either suggesting the Ancients would migrate and settle across different areas of the Earth's surface, or they would migrate and settle entire planets. If Sephiroth was suggesting the Ancients migrated and settled across Earth's surface, he should have said, "They would migrate and settle parts of the Planet, then move on to other areas..."
However, Sephiroth is suggesting the Ancients would migrate and settle the entire Planet itself. Once achieving this, they would move on to another planet until they find the Promised Land, a planet itself...
During the Temple of the Ancients quest on Disk 1, you'll encounter a bizarre humanoid creature in the maze. When you finally catch up with it, Aerith will comment,
"Those are the spirit bodies of the Ancients. They've been away from their planet for a long time to protect this temple."
Now seriously, what can this mean? Aerith says 'their planet' as if the creatures aren't from Earth. Space travel, anybody?
okay, if the Ancients did indeed travel in space, where are the rockets they must have built? Well, if you visit Bone Village, you'll find the wreck of an excavated fighter jet which is clearly beyond the technological levels of the Shinra Corporation. Perhaps the Ancients built this technological wonder?
The only other alternative is the Ancients travelled to other planets by 'star gates', a process probably very similar to Cloud's travel through the Lifestream during the ending. This is mainly speculation, but the game suggests the Ancients may have travelled in space one way or another. At least two statements have been found in the game supporting this fact.
The Shera (Sierra) airship in Advent Children and Dirge of Cerberus may be a Cetra starship, and it may also have originated on another world: specifically, Spira from Final Fantasy X.
According to the Final Fantasy VII Ultimania Omega, the Ancients came to the planet aboard a space craft of some sort. If you've played FFVII: Dirge of Cerberus, when you're aboard the Sherra, Cid's newest airship, one of the crew mechanics in the engine room tells you that Cid didn't build this airship. Rather, he excavated it from some ruins. If you look at the outside of the Sherra, its body resembles something you'd find in FFX...
The inhabitants of FFX built a spaceship and migrated to a distant planet, are, in fact, the Ancients of FF7.
If you want to read an interview with the writer of FFVII, FFX and FFX-2, Kazushige Nojima then follow this url:
http://www.willamette.edu/~ejohnson/nojima.htm
