Preatorian recruitment

Ok how i do i recruit the praetorin legion. I have trigerd the reforms and built everything to large city scale. I know you have to have the castra praetoriani in rome but the building does no show on the construction page. I have rome. i am playing the senate mission.
I have tried this in imperial campain playing as the senate thinking i could then recruit them. But still no joy.
Please help

thanks

There are various pre-requisites for that building, including farming levels and other things. Build all other buildings and it will appear.

Ok i will give it a go and look out for it.

Thanks

It's a farm level :)