MUNDUS. — With this term, in Rome, was designated a small pit dug on the Palatine, vaulted “in the likeness of the world above us” (Cato, apud Festus, 144), into which only one man could descend on the three days of the year (24 Aug.; 5 Oct.; 8 Nov.) when it was opened (Mundus patet; cf. Festus, s.v.).
Modern scholars (as did the ancients) attribute a twofold meaning to the m. In the first place, this pit, dug according to Etruscan rites governing the founding of cities, was meant to receive the choice grain for the new sowing (a fragment of Festus [126] says ... Cereris qui m. appellatur); it was indeed opened on the eve of the Opiconsivia, the feast of the grain stored in the granary; at the beginning of October, dedicated to the sowing of spelt; and finally during the sowing season for wheat. The second aspect of the m. is connected with the world of the dead. Varro says (apud Macrobius, I, 16, 18): “It is as if the gate of the sad and infernal gods were opened when the m. is opened,” its lower part being consecrated to the Manes (Cato, loc. cit.). For this reason, since the m. was like the meeting-point of the world of the living and that of the dead, and since it was feared that on the days it was open the souls of the dead would return to earth to spread their baleful influence, those three days were called “religious,” i.e. inauspicious for beginning any public or private undertaking (see also: MORTI, MONDO SOTTERRANEO dei).