[[WMG: Nemausus/Menausus, the third layer of Arcadia, didn't fall into Mechanus -- [[TabletopGame/{{Eberron}} it became Daanvi]].]]

Think about it -- the description of Daanvi sounds just like the description of Arcadia. Arcadia is a lawful and slightly-good plane, while Daanvi is a straight-up lawful plane. And how did Arcadia lose its third layer? ''That layer became too lawful.''