We study weakly disordered quantum wires whose width is large compared to the Fermi
wavelength. It is conjectured that such wires diplay universal metallic behaviour as long
as their length is shorter than the localization length (which increases with the width).
The random matrix theory that accounts for this behaviour - the DMPK theory- rests on
assumptions that are in general not satisfied by realistic microscopic models. Starting
from the Anderson model on a strip, we show that a twofold scaling limit nevertheless
allows to recover rigorously the fundaments of DMPK theory, thus opening a way to settle
some conjectures on universal metallic behaviour.