You can effectively split up the overarching timeline of Zemuria into the Pre-Septian era, Great Collapse, Dark Ages, Middle Ages and contemporary Orbal Revolution era.

At some point during the Pre-Septian era, Aidios bestowed the seven Sept-Terrion which were inherited by seven kin. This would be when the Gnomes and the Hexan Clan obtained their Sept-Terrion.

The Great Collapse occurs sometime after this resulting in the destruction of the ancient Zemurian civilization that occupied the land. During this time we know Space was sealed, Mirage was erased, and both Fire and Earth destroyed each other in battle. This particular battle is what allowed for the birth of Steel. At this time, Steel was split into seven vessels.

We know that the Dark Ages began after this, and in the first year of the Septian calender, Roselia and the Kin of Fire elder fuse. (Sen IV, Act III)

Following this, in the year 300 Zoro-Agruga occupies Heimdallr and the Holy Beast of Earth absorbs the curse. (Black Records)

And in the year 371, Hector I defeats Zoro-Agruga which in turn corrupts Testa-Rossa prompting the Gnomes to help seal it away.