Dungeonosophy
Legend
Huh. Not being particularly familiar with the "I" part of BECMI, I had no idea there was an official D&D version of "Magic Medieval Earth." Is WotI the only place it's mentioned? What's been said about it?
I don't have Wrath of the Immortals (WotI) with me. But here's a close summary of Laterre:
Okay, in the Classic D&D game universe (as expressed in the WotI boxed set), there are Dimensions, which are of a higher order than the Multiverse as such. Such as:
The Multiverse Dimension - includes the Material Plane, the Elemental, Ethereal, Astral, and Outer Planes.
The Old Alphatia Dimension
The Nightmare Dimension
The Vortex Dimension
The Dimension of Myth - contains Laterre. The source of "real world" mythologies.
Laterre is where the d'Amberville family came from. They're some of the most famous NPCs of Mystara. TSR borrowed the Ambervilles from Clark Ashton Smith's (CAS) Averoigne Cycle, which are part of the Cthulhu Mythos. In CAS' stories, the French province of Averoigne is a fictional replacement for the real-life province of Auvergne.
Of course "Laterre" is simply a modification of French "La Terre" (The Earth). There are also some Scottish Highlanders from Laterre who made it to Mystara. They speak "Kaelic."
There's a 2E-era web enhancement to Chronomancer which mentions the connections between Mystara and Earth - but the author (Roger Moore) confuses Modern Earth with Laterre. WotI says Laterre is specifically a magical medieval version of Earth. It presumably also has "Averoigne" province instead of "Auvergne."
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Also, properly Wrath of the Immortals boxed set isn't "BECMI" D&D, because the "I" part of "BECMI", namely, the Immortals Set (Gold Box), was replaced and revised by Wrath of the Immortals. RC/WotI D&D ("Rules Cyclopedia + Wrath of the Immortals") is basically the ".5" edition of Classic D&D.
Lastly, to clarify, when I said "the crystal sphere of Laterre", I didn't mean to imply that crystal spheres were part of the WotI cosmology (the Classic D&D Multiverse). I just mean that Laterre's equivalent in the 2E/5E crystal sphere cosmology would presumably be modeled on the medieval (European) Neo-Platonic spheres.