It's a long story... the Old Man is the planet, and the Old Woman the sun. In the last days on the surface, the sun became hotter, and the climate was affected badly. Deserts were flooding, farmlands suffering droughts, tides overrunning the seaports... and it just got hotter and hotter.
The Oracle of Ophiuchus brought people together, as many as possible, at the request of the gods, to create a shelter and protect them from the heat, while they tried to calm the Old Woman down. It was so hot by the time they gathered that they could only work at night, and slept during the day in cooled tents... the shelter was only barely completed in time to save those who did come together, and the ones who didn't arrive in time...