The only canon description of Praetoria comes from the box set
released in the 1990s. You can find that in the Files section of this
group under "PraetorianBoxsetBackground.rtf"
This (though possibly claimed by the poster) was actually posted by
Chosen Man in 40k Online, according to Col. Gravis:
http://uk.groups.yahoo.com/group/praetorian-IG/message/53
However, your best go is from Col. Gravis' own description also in the
files section named "Praetoria.doc"
Gravis, as you will soon learn, is His Majesty's Right Honourable High
Governour General Lord Admiral of Praetoria. He's your best source,
I'd say.

--- In praetorian-IG@..., "angloirishneovictorian"
<rozc19@...> wrote:
>
> Greetings fellow Guardsmen!
> I'm not new to the Praetorian scene, but I am to the web community...
> This time last year I realised there was no background that anyone had
> ever written about Praetoria (bear with me, I know better now) and
> decided to hammer some together for myself. I sent a copy of my
> document to the Black Library, but they never replied. A few weeks ago
> I joined the Boot Camp Forum, to gain advice from my fellow guardsmen.
> My quest yielded little, but by happy chance I encountered a link to
> this group.
> What I'm basically trying to find out is; What background for our brave
> Pith-Helmeted troops is there? Where can it be found? Is it canon? has
> all my work been in vain? And is this really Home Brew I'm sipping - or
> is it something else?
>
> Here, at least, is my version of Codex Praetoria.
> http://z4.invisionfree.com/Boot_Camp/index.php?showtopic=7930
>
> cheers,
> AINV
>