The Jewish mourning calendar's graduated stages are not a modern arrangement; its structure of an initial intense period followed by successively longer, less restrictive stages is worked out in detail in the Talmud, compiled in the first several centuries of the common era, which is why its specific milestones, seven days, thirty days, and a year for a parent, carry the weight of a fixed legal schedule rather than a general custom that individual families may adjust freely.
Catholic tradition took a different route to its own recurring commemoration of the dead: the observance of All Souls' Day, a fixed annual day of prayer for the deceased broadly, is traditionally credited to Odilo, the abbot of the monastery of Cluny, who established the observance for his own monastic community around the end of the tenth century, and the practice spread outward from Cluny's considerable religious influence to become general practice across the Western church. Much more recently, the twentieth and twenty first centuries have added an entirely new form to this landscape, the secular memorial or celebration of life service, developed largely outside any religious calendar as families and funeral professionals sought a format for households with no fixed religious mourning schedule to follow, typically compressing what older traditions spread across weeks or a year into a single gathering held once, soon after death.