The San d'Orian mission storyline follows the pursuit of Lightbringer, a legendary sword that Ranperre D'Oraguille used to "tame the beasts that wreaked havok" - an alternate to this storyline explains how the Elvaan tribes were freed from Tarutaru subjugation on Quon by discovering TWO artifacts, one held by Ranperre, the other by the founding father of Tavnazia. Focusing on Lightbringer for now, its physical appearance resembles a halfbreed of metallic workmanship similar to the ruins of Alzadaal (look at the hilt) and some sophisticated technological blade. When unsheathed, it will "absorb energy from its surrounding environment and transform it into a force more powerful than any other." When unsheathed, the holder describes a feeling as if all other life is insignificant (Rochefogue) and as if they were a god (Trion). The pollen from a Dream Rose can subdue the sword's power for a short time.
Secondly, Tavnazia and Aht Urghan have had a long standing relationship, up to the point when Tavnazia was destroyed by the unsheathing of Lightbringer; after which the ambassador from Tavnazia residing in Aht Urghan was promptly kicked out. From this point on, up to the point where the San d'Oria missions begin, Lightbringer is lost. The location of the other artifact is never revealed.
Now for the speculation: The second artifact is the Gordeus, relinquished by Tavnazia to Aht Urghan for study. Sage Walahra studies it, and discovers its true importance, but the Crystal War and the conflict with the Far East prevents any action to be taken. I speculate that Lightbringer is actually the master control "animator" for Alexander, and that Emperor Alzadaal actually wielded it to this purpose waaaaay back in the day. Unsheathing Lightbringer causes a part of Alexander to awaken and causes the destructive force; while the Dream Rose forces Alexander back to slumber. Lastly, there is a definite connection between Lightbringer and mechanical beings; as the Orcs desired to merge Lightbringer with a warmachine to make a more powerful weapon.
The Gordeus and Lightbringer both have been spoken of as being a key to unlocking the origins of all beings, so they are probably connected in some fashion - perhaps all of the problems in Aht Urghan will end once Lightbringer is used to pierce the Gordius.