Isthmus of Lustria
The Isthmus of Lustria is loosely analogous to the region around Panama in the real world.
Per square mile, the Isthmus of Lustria is the most densely pack region of Lustria with mystic ley lines and monuments to the Old Ones.
The exposed location of the Isthmus would theoretically leave the region vulnerable to outsiders but this region of Lustria is probably the safest for the First of any other region of comparable size simple because of how heavily patrolled it is.
The geographic and political center of the Isthmus is the Temple City of Hexoatl, the City of the Sun. The entire Isthmus is part of the official protectorate of Hexoatl and by extension Slann Lord Mazdamundi. If any of the Slann here disagree with Mazdamundi, they probably keep their telepathic mouths shut.
Not only is the region heavily patrolled by armies of Sauri and Skinks but a large population of unusually active Slann with access to a lot of intact monuments harnessing the power of magical ley lines means that Mazdamundi have the embarrassment of riches in that they can crush enemies in the region with either magic or armies as they see fit.
Ecosystem
Despite being unique in terms of the Lizardmen inhabiting the region, I don't believe the Isthmus of Lustria differs significantly from the the Lustria norm, aka the Great Jungle.
Given that the region is smaller geographically, the First of Hexoatl have to be more careful with harvesting resources from the jungle lest they overtax their local ecosystem, but this is only a minor inconvenience.
Compared to other temple cities, Hexoatl is micromanaged so they certainly have efficient farming and similar infrastructure in place and with an active and powerful Slann population they could life magic to accelerate regrowth if a localized area has an "oopsy" and suffers non-supernatural ecological damage.
Climate
Hot and humid like everywhere else in Lustria. The Isthmus has two massive oceans on both sides which produces a lot of moisture, but without the Spine of Sotek mountains acting as a rain shadow or wall, rain clouds tend to move in an out pretty quickly.
In my head canon, the difference between the "wet" and "dry" seasons of Lustria are less pronounced here.
History
The Isthmus of Lustria, at least in my head canon is the safest place in Lustria...for Lizardmen.
They suffered losses in the Great Cataclysm (which ruined Pahaux) but no major loss occurred here since though it is possible there could have looting or desecration by surprise looters in some of the outlying regions.
In my head canon, the fact that the Isthmus of Lustria has suffered fewer great losses than the rest of Lustria has resulted in Lord Mazdamundi having an aggressive overall strategy for fulfilling the Great Plan, he is not in a particular hurry. Given that Mazdamundi wants to evict all humans back to the Old World, Port Reaver and Swamp Town are on borrowed time and it's only a matter of time before the axe falls.
Also, given that incursions that do happen are dealt with very quickly, most of the Slann and their minions have not had much time to study their enemies. This is why the Lizardmen here rarely if ever draw any distinctions between the High Elves and the Dark Elves or the Empire and the Warriors of Chaos. All elves/all humans look alike to them. Whereas to Lizardmen in other parts of the Lustria there is a large distinction between Fallen and Anathema that dictates what kind of response they are likely to commit against incursion.
Outside of the Great Cataclysm where Daemons were the Lizardmen's greatest foes and the Time of Sotek where the Skaven were the Lizardmen's greatest foes, the First mostly have to deal with Dark Elf raiding parties and human dominated treasure hunting expeditions.
There is no official account in published works of a major Dark Elf incursion against this region and according to my head canon, I imagine Malekith or Morathi have issued a proclamation warning their minions that attempting a casual raid on the Isthmus of Lustria is suicidal.
I suppose Malekith and/or Morathi have the resources and mystic might to seriously challenge Mazdamundi and launch a devastating massive invasion of the isthmus, but Malekith isn't likely to commit this much of his resources for an large scale attack against some target other than Ulthuan though Malekith versus Mazdamundi would be an epic story.
It is vague in official sources how much outsiders know about what is going on in Hexoatl or the outlying region, but in my head canon, while outsiders may not know "There is a powerful and active ancient Slann named Mazdamundi that runs this region like an efficient engine of death" the outside world must have pieced together some clues.
I figure the High Elves of Ulthuan and the Dark Elves of Naggaroth must know that this is a region of potent and dangerous magic. Their wizards are too powerful and well organized not to have sensed some of what is going on here. Add to the fact that there is enough espionage between these two nations, if one elf nation finds out a geographic secret, chances are the other will learn this secret eventually.
For their part, the casual human raiders of Lustria might have noticed that while well over half of expeditions to Lustria never return, expeditions to the Isthmus of Lustria have an even lower success rate.
Human adventurers seem more foolhardy than Elven adventurers so a few Human groups probably invade here anyway, or they may land here by accident after their ships are blown off course.
Normally in published GW works, the Warriors of Chaos are single-mindedly focused on destroying the Empire of Man. Hypothetically, if the forces of Chaos decided that the Lizardmen need to be taken out of play, Hexoatl would relatively easy for a Chaos invasion fleet to sail towards and breaking Hexoatl would definitely cripple the Lizardmen as a whole.
Mazdamundi against Anerion the Everschosen or some other Warrior of Chaos heavy weight would also be an interesting story, and it would be more plausible than Mazdamundi versus Malekith.
Type
Isthmus
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Included Locations
Owner/Ruler
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