Q:

Grammaticality: 'something than which nothing greater can be thought'

Source: pp 158-159, The Cambridge Companion to Anselm, by Brian Davies, Brian Leftow

What Anselm describes himself as looking for here he believed he had
  found when reflecting on the idea that God is "something than which
  nothing greater can be thought" (aliquid quo maius nihil cogitari
  potest).

The bolded looks wrong. How can something (a pronoun) precede than (a preposition)?
Why was the bold not written as: something OTHER than which?
Surprisingly, Google reveals no other context with this syntax (which I first encountered here)
PS: I reorder the first two sentences in the quote to facilitate understanding:

[Anselm] believed he had found
  [w]hat Anselm describes himself as looking for here[,]  when reflecting [...]

A:

It is a word order that was once far more common than it is today. 

[Source:] He suppressed all his letters of recommendation, which he justly concluded would subject him to a tedious course of attendance upon the great, and lay him under the necessity of soliciting preferment in the army, than which nothing was farther from his inclination;

Tobias Smollett on Google 

A:

God is something. 
What kind of something?
We talk about this something, so with a relative clause 

1. it is something which we think about.  

We have a name for this something, so with a relative clause and pied-piped preposition 

2. it is something for which we have a name.  

Now let us reconstruct the sentence questioned in the OP:

We cannot think anything [to be] greater than this something. 

  Since cannot ... anything = can ... nothing,   3 is equivalent to 

We can think nothing greater than this something. 

  By passivization 4 becomes 

Nothing can be thought greater than this something    

Finally, rewrite 5 with a relative clause and pied-piped preposition 

it is something than which nothing can be thought greater.

A:

(This is actually similar to the two existing answers. I'd like to make the structure more obvious.)
The clause in the question should become obvious if we rewrite it as two clauses:

God is something than which nothing greater can be thought
  = [ God is something ] + [ Nothing greater than (that thing) can be thought ]
(Also note that, as LePressentiment suggests below, God is something which nothing greater than can be thought would be another possible rewrite.)

Another note: think being used transitively is common enough, e.g., We think the same. You think what? Think Green.

