It is true that the Rigveda does not provide us details of the inner layout of these forts, but surely the text was not meant to be a treatise on Vastusastra. May it be remembered that it is essentially a compilation of prayers to gods and should be looked at as such. All the evidence that it provides regarding the material culture of the then people is only incidental.

Aryan invasion of India: perpetuation of a myth, In: Edwin F. Bryant and Laurie L. Patton Indo-Aryan Controversy: Evidence and Inference in Indian History. — 1st ed. — London: Routledge, 2005. p.67.