Its location is uncertain. It was usually sealed by a stone lid known as the "lapis manalis". On August 24, October 5 and November 8, it was opened with the official announcement ""mundus patet"" ("the "mundus" is open"), and offerings were made there to agricultural or underworld deities, including Ceres as goddess of the fruitful earth and guardian of its underworld portals. Its opening offered the spirits of the dead temporary leave from the underworld, to roam lawfully among the living, in what Warde Fowler describes as ‘holidays, so to speak, for the ghosts’. The days when the mundus was open were among the very few occasions that Romans made official contact with the collective spirits of the dead, the "Di Manes" (the others being Parentalia and Lemuralia). This secondary or late function of the "mundus" is attested no earlier than the Late Republican Era, by Varro. The jurist Cato understood the mundus' shape as a reflection or inversion of the dome of the upper heavens. Roman tradition held that the "mundus" had been dug and sealed by Romulus as part of Rome's foundation; Plutarch compares it to pits dug by Etruscan colonists, containing soil brought from their parent city, used to dedicate the first fruits of the harvest. Warde Fowler speculates the "mundus" as Rome's first storehouse ("penus") for seed-grain, later becoming the symbolic "penus" of the Roman state. In the oldest known Roman calendar, the days of the "mundus" are marked as C(omitiales) (days when the Comitia met). Later authors mark them as "dies religiosus" (when no official meetings could be held). Some modern scholars seek to explain this as the later introduction and accommodation of Greek elements, grafted onto the original "mundus" rites. The rites of August 24 were held between the agricultural festivals of Consualia and Opiconsivia; those of October 5 followed the "Ieiunium Cereris", and those of November 8 took place during the Plebeian Games As a whole, the various days of the "mundus" suggest rites to Ceres as the guardian deity of seed-corn in the establishment of cities, and in her function as a door-warden of the afterlife, which was co-ruled during the winter months by her daughter Proserpina, queen-companion to Dis. In Roman theology, prodigies were abnormal phenomena that manifested divine anger at human impiety.