This is the first opening of the mundus - a concave pit that was originally dug on the founding of Rome (i.e., on the very first Parilia). The mundus, an image of the inverted sky placed into the earth, was located either in the Comitium or at the centre of the Quadrata Roma (the Palatine). The lapis manallis that covered the mundus was removed (mundus patet) on 24 August, 5 October and 8 November as a symbolic means to allow the di manes of the underworld an entry into the upper regions of the earth. In essence, this was an attempt to provide an outflow of infernal pressures and relieve thereby the increasing solar tensions that might otherwise accrue as the sun spends increasing time below the horizon. Subconscious or subterrranean agitation is thereby given a vent for release.

Sometimes confused with the umbilical urbis or symbolic centre of Rome and sometimes with the 'tomb of Romulus' which Caesar covered with a lapis niger when the Forum was paved, the mundus is a Panda Cela (ea quae panditur et ea quae celat) - an opening and closing link between the community and the underworld dead.