OK just found what are images 5 and 6 !
In Pompeii there is a temple to Jupiter with an "eternal torch" (5th). If the torch goes out, it will anger Jupiter (6th).
The goal is to save the torch.
Lava is blocking path extending the journey, Ashes threatens the torch. And time runs out !
I have now the complete "story" of the game. Next step : play with cards to "translate" this in mecanichs.
See you !