@TinCres Thanks for asking. The Medusa heads are so called spolia, reused blocks from an unknown older building. Whether their orientation in the cistern had any meaning at all is highly unlikely, but not impossible. But as the depiction of the Gorgo Medusa had a protective function in Greec and Roman times, and given that this meaning was not forgotten in the 6th century, when the cistern had been build, it would not make much sense to "invert" it anyway. Hope that answered your question.