  We embed a new three-form vector multiplet in ${\cal N}=1$ supergravity and
we show that it can be used to generate dynamically the Hilbert--Einstein term.
We then recast the theory into the standard Freedman model and we argue that a
pure Fayet--Iliopoulos term is in tension with the weak gravity conjecture.
Finally, we couple the three-form to a super-membrane and study BPS domain
walls within matter-coupled supergravity. In these models, the Planck mass
takes different values on the domain wall sides.
