San Francisco de Asis by Francisco de Zurbarán, c. 1660
The Triduum of Hallowmas is a three day observance in the Catholic (and the greater Christian) church: All Hallows’ Eve (31 October), All Hallows’ Day (1 November), and All Souls’ Day (2 November).
All Hallows’ Day (also known as All Saints’ Day) is when the church honors all the saints—those known and those unknown. It is believed to have started around the year 609 when the Pope (re-) dedicated Rome’s Pantheon to Mary and all the martyrs. By this time, the Pantheon had already been a Roman temple honoring all the gods (“The Pantheon”) for some 400 years.
In parts of the world, on All Saints’ Day, it is customary to visit the graves of loved ones, decorating them with flowers and praying before them.