In the poem ‘O Fortuna’ (anon., 13th c., but made famous by Carl Orff’s setting), there is this verse:

> 
> *Quod per sortem  
> 
>  sternit fortem  
> 
>  mecum omnes plangite!*
> 
> 
> 

This is typically translated as ‘since luck strikes down the strong, everyone, weep with me!’ or something to that effect. I am confused about the use of ‘per sortem’ (prep.+acc.) for what seems to be the subject of the *quod*-clause. At first I thought it was some form of passive voice, but *sternit* is conjugated in the active.

I cannot seem to find any other examples of this usage of *quod per*. Is it even grammatical?