Aulus Gellius, Attic Nights 13.11.1-2
lepidissimus liber est M. Varronis ex satiris Menippeis qui inscribitur ‘nescis quid vesper serus vehat’, in quo diserit de apto convivarum numero deque ipsius convivii habitu cultuque. dicit autem convivarum numerum incipere oportere a Gratiarum numero et progredi ad Musarum, id est proficisci a tribus et consistere in novem, ut cum paucissimi convivae sunt non pauciores sint quam tres, cum plurimi non plures quam novem.
The book of Marcus Varro, from his Menippean satires, which is entitled ‘You don’t know what the late evening might bring’, is most charming; in it he discusses the appropriate number of dinner-guests and the ordering and arrangement of the dinner-party itself. He says that the number of guests ought to begin from the number of the Graces and go on until that of the Muses – in other words, it should start out from three and stop at nine, so that when the guests are fewest they are not fewer than three, and when they are most in number they are not more than nine.