The mental ray architectural library contains a set of shaders designed for architectural and design visualization.
The most important are the mia_material(_x), an easy to use all-around general purpouse material, and the Physical Sun and Sky along with the portal light shaders.
The library also contains many other tools, like shaders for...
In standalone mental ray the shaders are added by including the "mi" declaration file and linking to the library;
link "architectural.dll"
$include "architectural.mi"
The library is supported in mental ray version 3.6 or newer and will not function on earlier releases of mental ray.