In a difficult passage of a difficult work by an eighth-century author who may have been a southern Italian (Ionian?) cleric with excellent Carolingian connections, and who is conventionally called Aethicus Ister, the water cycle is minutely described. Using obscure, erudite language this cosmographer claimed that the winds performed an important service by lifting “a very dense haze” from the seas and transporting this vapor to the tops of mountains, giving birth to rivers when it reached the cold crags. From a modern scientific point of view, Aethicus was very close to an accurate portrayal of how the water cycle works. He offered an “atmospheric” explanation to the puzzle of why water wends endlessly downward to the sea, without ever seeming to rest or run out, and why the sea, despite this constant inflow, never (or only in extraordinary moments) brims over and spills onto the land.

But Aethicus was not content with so simplistic a model. It did not account for the existence of springs, where water burst through the surface of the earth from below. Aethicus therefore confidently described a process whereby much water flowed underground through fissures and channels which led it from the sea back to the highlands where it could surface in springs, to begin its headlong dash down to the beaches again, this time in the open air. He knew that the “bitterness” of sea water was lost during its hidden, cavernous journey by a leaching process.