I'm doing the Miner's Guild induction quest right now and have the text on my screen. In case anyone wants to read it:
Nenekko:
I see. Sil'dih must have been a truly vast city at its peak, just as the histories say.
Oh dear, forgive me for not explaining. I assumed you knew.
Sil'dih was an ancient city, located very near to Ul'dah. At one time, it prospered much as Ul'dah does now, but they lost a great war and the civilization crumbled.
To this day, none know precisely what kind of city it was.
But to gaze upon the sheer scale of the ruins, one can only imagine that it must have been as great and lively a city as our own.