mundus patet - the mundus was a ritual pit which had a sort of vaulted cover on it. Three times a year the Romans removed this cover (August 24, Oct. 5 and November 8) at which time the gates of the underworld were considered to be opened and the manes (spirits of the dead) were free to walk the streets of Rome.
ludi Augustales scaenici (day 1 -- from 11-19 A.D. and post 23 A.D.)
ludi Augustales scaenici (day 3 -- from 19-23 A.D.)
287 A.D. -- martyrdom of Palmatius