Ancient Civilizations in Eorzea

Trying to count them, so far.

1. The Great Allagan Civilization. Seems mostly based in Mor Dhorma but has outposts elsewhere.
2. The ones behind the Floating City of Nym in upper and outer La Noscea. Probably also behind the ruins in Camp Bronze Lake and the Wandering Palace.
3. The Amdapuri Civilization (Gelmorrans?). Located in the South Shroud and responsible for all the ruins there including Totorak and Amdapur Keep.
4. The civilzation in Southern Thanalan. Responsible for the Sepulchre, the Sunken Temple of Qarn and the Labyrinth.

Not sure if there is anymore.

Its not clear if these civilizations coexisted or existed and lived in different Astral Eras, but they probably died during the Umbral Eras.

Everything around Bronze Lake is part of Nym, including Wanderer's Palace. Its explicitly shown through the Scholar Questline; and the final battle takes place in WP.

Also it seems native Nymians were Lalafell.

I read somewhere a disease turned the Nymians into tonberries. Poor lala...

The loremasters would be able to clarify this, but from what I'm aware, these are the known ancient civillizations that formerly existed in Eorzea:

1. The Allag Empire. Probably the most famous, this was believed to have gained control of virtually the entire continent of Aldenard at it's height. Both technologically and magically advanced, some of their ruined structures can still be seen in the present day (the Crystal Tower and it's related structures is the best known, but the Royal Allagan Sunway and Starway roads leading out of Ul'dah were also built by them). The SMN Job originated in Allag. The Allagan Empire also were the ones who bound Bahamut within Dalamud and sent him into outer space, and also

constructed the Ultima Weapon as a Primal-killer.

Allag was considered so advanced, it's been stated that their level of science, technology and aetherial manipulation even exceeds Garlemald's technological level, no mean feat.

2. The Kingdom of Nym. A nation that flourished on the island of Vlybrand, they were masters of arcane arts. The SCH Job originated in Nym. They were stated as being a not particularly large country, but made up for their small size in sophistication. The Wanderer's Palace at Bronze Lake and the Floating City of Nym, both in La Noscea are two of their best known surviving structures. It is believed they worshiped Oschon the Wanderer, the god of the mountains and vagrants as their guardian, as the name 'the Wanderer's Palace', and the fact Oschon's glyph is set onto the floor at the entrance to the palace, definitely suggests this.

3. The Sultanate of Bel'ahdia. A nation that seemed to predate Ul'dah in the Thanalan region in the early Sixth Astral Era, they seemed to worship Azeyma the Warden, the goddess of the Sun, as their surviving structures, such as the Invisible City near the Golden Bazaar, the ruins near Vesper Bay called 'The Silent King', and the spectacular structures at Highbridge all possess Azeyma's glyph. Evidently contrary to popular belief, the Sunken Temple of Qarn actually seems to pedate Bel'ahdia, as the Duty Finder mentions the ruins appear 'far older than this Sixth Astral Era civilization', and that 'Bel'ahdian sultans each added to the original structure'. Thus Qarn seems to have been built by an earlier society (Allag?).

4. The Underground City of Gelmorra. In 1.0 this was probably the most enigmatic of the ancient civilizations that had flourished in Eorzea - the mysterious circular ruins in the North Shroud that bear it's name is probably the most well known surviving relic from this society, although other ruined structures in the Black Shroud were also Gelmorran, such as the Tam Tara Deepcroft and the Thousand Maws of Toto-Rak (apparently). What is known now is that Gelmorra originally was a civilization of elezen, who were forced to live underground by the elementals that inhabit the Shroud. It was only once the moogles interceded on the Gelmorrans' behalf, that they were allowed to live on the surface, allying with the newly arrived hyur and thus resulting in the founding of Gridania under the elementals protection - naturally Gelmorra was abandoned after this, with the forest gradually reclaiming Gelmorran structures, although some were re purposed (like Tam Tara). Although not proven conclusively, it seems the Gridanian flag seems to have had a prototype in Gelmorra's flag, as a predecessor to it shows up within certain Gelmorran ruins (only lacking the lily on top, replaced with different shape of flower).

5. The nation of Amdapor. Only known from two enigmatic structures in the South Shroud (Amdapor Ruins and Amdapor Keep), some believed that this was actually part of Gelmorra, but the Duty Finder entry for the Amdapor Keep seems to suggest otherwise - that they were a brief nation founded by mages who ended up destroying themselves with the spells they unleashed. It also seems that the nation was there without the permission of the elementals, hence following the destruction of the Amdapori civilization, the elementals hid the ruins under the trees so that it's secrets would not be found, until the Calamity undid that and the Lambs of Dalamud cult moved in naturally.

6. The sultanate of Sil'dih. Probably the most recent 'fallen' nation, Sil'dih seemed to have been founded at the same time Ul'dah was, and was even stated as being Ul'dah's 'twin' in 1.0. However, as Thanalan gradually desertified, water supplies became scarce and soon the two nations ended up going to war against each other to secure the precious resource, which Sil'dih lost (after desperation forced them to resort to no less than necromancy to revive their fallen soldiers to continue fighting, which caused a zombie apocalypse). When the fighting ended after the zombies effectively destroyed Sil'dihian society the ruins were sealed and buried, which by the time of 1.0 only an abandoned aqueduct and a mirage of the city often seen shimmering in the distance the only hint of the once proud city that once shared the desert with Ul'dah. By the time of ARR the ruins however have been partially excavated, although they remain just a jumble of broken stonework at the bottom of a gorge in Central Thanalan.

Anyway, that's what I understand of Eorzea's past civilizations anyway - I'm sure there's plenty that I've missed or otherwise gotten wrong, so please feel free to correct me! :D

Enkidoh's post is quite thorough. The one thing I'll add is that while running through the SCH relic quest, I thought I saw a passing mention that the Nymians and Amdapori were actually coeval and didn't get along/were at war. Something about a surprise beach raid by the Nymians on a host of Amdapori soldiers. That would need to be fact checked by someone though. If I'm right about that text existing, it would have been from Gerolt if someone can data mine his dialogue out to confirm it.

Can you pull it up in your journal?

Found the text. It's not in the in-game journal, but XIVDB has his dialogue, thankfully. The relevant snippet comes after defeating the Hydra.

Quote:

Originally Posted by Gerolt

But what's done is done...or in this case, not done. Anyroad, let's talk about that text ye brought. It contains accounts o' the major clashes what took place durin' the War o' the Magi. The entry on the Battle o' the Gods' Grip jumped out at me. This was when the Nymians took the Amdapori host by surprise as it made its beach landin'─takin' the siege to the besiegers, as it were. As they're wont to do, the scholars played a key role in the victory, though that didn't interest me near as much as the passage what touched on the Omnilex.