The subcaste or commensal group was the direct evolutionary product of the pre-existing tribe.

Its size was limited by the fact that its members had to meet at the periodical sacrificial feasts, by which their unity and the tie which bound them together was cemented and renewed.

As already seen, when members of a subcaste migrated to a fresh local area, and were cut off from communication with those remaining behind, they tended as a rule to form a fresh endogamous and commensal group.

Since the tie between the members of the subcaste was participation in a sacrificial meal of grain cooked with water, and as this food was held to be sacred, the members of the subcaste came to refuse to eat it except with those who could join in the communal feast; and as the idea gradually gained acceptance, that a legitimate child must be the offspring of a father and mother both belonging to the commensal group, the practice of endogamy within the subcaste became a rule.
92.

Veneration of the caste implements.
Since all the citizens of the Roman State participated in a common sacrifice, they might be considered as a single caste, or even a subcaste or commensal group.