The motto translated from Latin reads: 'The things that are in the realms above are also in the realms beneath; What heaven shews is often found on earth. Fire and flowing water are contrary one to other; Happy thou, if thou canst united them: let it suffice thee to know this!'
The 7 terrestrial metals & planets are symbolized by 7 figures sitting in the cavern. The six Muses=metals surround Apollo in the alchemical hells. Sun and Moon Fire and Water united in the Hexagram The Four Elements represented in the corners.