That theme is literally the 'main theme' for the entire series - it's usually named simply Final Fantasy, but has also been titled as The Prologue.
The version of 'Final Fantasy' arranged by Masayoshi Soken however isn't the first version of that track to be used in FFXIV - 1.0 had a completely different arrangement made by Uematsu himself, called Opening Theme ~ Remembrance, which appeared on the FFXIV ~ Field Tracks, FFXIV Eorzean Frontiers and Before Meteor albums (in 1.0 it played during character creation). But yeah, that version is the ARR version, and is not the same version that appeared in 1.0. Just thought I'd clarify that for those who didn't play 1.0.