Honorouring the Spirits of the Ancestors in Ancient Rome: Parentalia (February 13～21)

In ancient Rome, the month of February was a busy month when it comes to "feriae" (religious celebrations). Many feriae were related to the ancestors in one way or another.

From February 13^th to February 21^st , there were a series of rituals and festivities called the Parentalia. [I] During this period, the Spirits of the Dead, or Di Manes, were believed to come back to the world of the living. [II]

 

The poet Ovidius warned his contemporaries that neglecting the Di Manes, would have consequences: He wrote that once, when the Romans happened to be at war during the Parentalia, they failed to pay their respects at the tombs of the deceased and that night, the "Snimae" (Spirits) came out of Their tombs and voiced Their discontent, howling through the streets of Rome.

The people made sure to conduct the appropriate rites from then on. [III ]

However, even if the spirits were pleased, there was a certain danger associated with Their arrival, because -for at least a certain period during the Parentalia- marriages were not allowed and the temple doors were closed to shield the Gods from the spirits of the dead. [IV]

This kind of taboo also exists in other polytheistic traditions:

In native Japanese “path of the Gods” “Shintō”, it is also customary to shield the Deities from the pollution that is caused by the dead: When someone has passed on in a certain household, the household shrine known in Japanese as kamidana is covered up with a piece of paper for the duration of the mourning period. [V]

References: 
[I] Beard, Mary et al. (1998) Religions of Rome: Volume 2, A Sourcebook. Cambridge University Press: p122.[II] Ovidius. Fasti: Book II: 565.
[III ] Ovidius. Fasti: Book II: 548.[IV] Ovidius. Fasti: Book II: 557.
[V] hakkouden (2016)『神棚封じについて』”Kamidana-fuuji ni tsuite” on youtube.com < https://www.youtube.com/watch?v=mthNPy6wrfA&t=54s> (retrieved February 12, 2018)