MUNDUS. - By this term there was designated at Rome a small pit, dug on the Palatine, with a vaulted ceiling “in likeness of the world above us” (Cato, in Festus, 144), into which only one man could descend on the sole three days of the year (24 Aug.; 5 Oct.; 8 Nov.) on which it was opened (Mundus patet; cf. Festus, s. v.).
Modern scholars (as already the ancients) attribute a twofold meaning to the m. According to the first, this pit, dug according to the Etruscan rite that presided over the founding of cities, was intended to receive the grain selected for the new sowing (a fragment of Festus [126] says ... Cereris qui m. appellatur); indeed, it was opened on the eve of the Opiconsivia, the festival of grain stored in granaries; at the beginning of Oct., consecrated to the sowing of spelt; and finally at the time of wheat sowing. The second aspect of the m. is connected with the world of the dead. Varro says (in Macrobius, I, 16, 18): “It is as though the gate of the mournful and infernal gods were opened when the m. is opened,” the lower part of which was consecrated to the gods Mani (Cato, loc. cit.). Consequently, since
the m. was like the meeting point between the world of the living and that of the dead, and since it was feared that on the days when it was opened the souls of the dead would return to earth to spread their malign influence, those three days were called religious, that is, inauspicious for undertaking any action, whether public or private (v. MORTI, MONDO SOTTERRANEO DEI).