Demeter and Semele.

Demeter is the Greek earth-goddess. One etymology I've come across makes Demeter  a worn-down version of Ida-Mater -- mother of the forested mountain (for Ida, I'm using Robert Graves' translation).

Compare this to Roman Rhea Silvia, consort to Mars; her name can be glossed as "earth-goddess of the forest". Mars is also associated with the Sabine Nerio, who is connected to the Germanic watery-earth-goddess Nerthus. The rape of the Sabine women is usually cited as the Roman version of the 'war of the functions'. Roman Mars and Sabine Nerio get married, somehow uniting the functions.

Rhea Silvia is said to be a vestal virgin, the mother of Romulus and Remus by Mars, who was later tossed off the bridge and drowned in the Tiber, as consort to the river god Tiber.

In his earliest form, Mars seems to have been a sky god, and in some ways, more important than Jupiter.

As outlined in an earlier posting, Greek Semele is a reflex of the PIE word for 'earth'. While Semele is normally thought of as a lunar goddess, there is a jumble of convergent and conflate myth here. Zeus is Sky-Father, Day-Father, and is not normally an explicitly solar deity, but in the myth of Semele, he is as solar as any god can be, burning poor Semele to a crisp. The child of their union is Dionysus. You have the sun burning Moist Mother Earth.

The children of Mars and Rhea Silvia are Romulus and Remus. Is it too hard to imagine an earlier version of the Zeus-Semele myth where the offspring are also twins? By Leto, Zeus fathers Apollo and Artemis; by Leda, he fathers Helen and the Divine Twins. With the Divine Twins, one of the twins gets killed; Romulus murders Remus.

I'm not ready to make any particular conclusions, but there seems to be something consistently old here, something we might call proto-Indo-European.

Mark.