Why did they use vertical trade lanes?

[Australopithecus]

That's also part of "some" of those theories. There're multiple layers which connect to. So you go down, up and such. No lights, no nothing.
Space game but same thing. We got upper lane, lower lane. Right one, left one. We don't have a 4D lane...
The question is, why Gallia uses Right-Left Trade Lane.

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