From FFXI Wiki

Shadowreign is the period of time of The Crystal War during which the Shadow Lord was at his most powerful. By utilizing Cavernous Maws and certain spells, players can visit certain areas of this past Vana'diel. The lands of the Shadowreign era are divided into war fronts, akin to the regions in present-day Vana'diel, and players may only visit ares of the Middle Lands (Quon and Mindartia) during the Shadowreign era. To distinguish them from their present-day counterparts, Shadowreign areas are designated by a "(S)" at the end of the area's name.

The fronts in Quon are:

The fronts in Mindartia are: