What Is Supergravity?

The idea of super symmetry, uno symmetry between bosonic and pemionic degrees of freedom was some er, i don't remember all this history. Then the idea of a, using that to have a theory with particles, with permionic particles, along with a graviton like thing, that was the sort of supergravity idea. And then, but then, somehow, somewhere in the middle of that, supergravity only in 26 dimensions and so on. When was that was that was not known from the beginning?