Terra

She appears, for example, on the altar of Augustan peace, where she is sitting with flowers and produce in her lap and two babies in her lap.

And this is normally understood to be Mother Earth, Terra Mater.

So we've got the heavens, the earth, the solar movements.

On either side of Mother Earth, just slightly at the feet of our central figures, we have on one side Apollo riding a griffin and on the other side, Diana riding a stag.