There's barely mention of the city in the histories, and none still live who remember it. But it was a beautiful city once, and prosperous. And now it is gone. Forgotten.Nenekko
Sil'dih (古代都市シラディハ, Kodai Toshi Shiradiha?) was a city-state that existed long ago beside Ul'dah in Final Fantasy XIV. It existed in Thanalan as a sister City-state to Ul'dah, both having been born from Belah'dia, but vanished from sight until the Calamity exposed the sealed ruins. Like Ul'dah, it was ruled by Lalafell.
History and locations
Sil'dih was ruled by the King of Springs, King Lalawefu. His financial reforms brought the city-state prosperity, but a combination of tax increases and untimely droughts led to civil unrest. The flood control developed by this nation soon drew the attention of the parched Ul'dahn citizenry, and a de facto war broke out.
The two nations were equally matched, until Ul'dahn thaumaturges devised a powder capable of turning the dead into zombies. Ul'dah used their catapults to cast the powder inside the city in order to have the dead attack the living. To explain the anguished screams, Ul'dah fabcricated a tale that Sil'dih had started turning their dead into zombies in order to win the war. This was used to justify an official declaration of war, and in their triumphant crusade sealed the gates of Sil'dih, wiping them out with their own perverse plague.
Ruins of Sil'dih can be visited in Central and Western Thanalan, recently uncovered during the Calamity. Before the rediscovery of these ruins the civilization was nearly forgotten. However, thanks to the daughter of the Amajina & Sons Mineral Concern's leader, Nenekku, and other Eorzean researchers such as Erik in the Monk quest line, much of the above history is now optionally available.
A remnant of the Sil'dih Aqueducts (likely relevant to the aforementioned flood control) was hidden in the furthest tunnels of the Copperbell Mines, which was not instanced in 1.0. It was later blocked by a strange wall of webbing, and only available via temporary Aetherial Gates during the first of the Lambs of Dalamud events. After this particular event ended the Sil'dih Aqueducts remained sealed.
The aqueducts were accessed again by the Scions of the Seventh Dawn when they were accused of murdering Nanamo Ul Namo and had to flee Ul'dah. They accessed the waterway via a secret entrance in Nanamo's private chambers, and the exit led them to the Sil'dih Excavation Site in Central Thanalan, north of the city.
The grandness and elegance of the aqueducts suggested Sil'dih rivaled, or even surpassed, Ul'dah in architectural aptitude. That they were more-or-less forgotten until recently suggests Ul'dah wanted to forget them and tried to erase them from history, or that they either lacked the means or motivation to keep adequate records.