The tribe, like the family and the phratry, was set up to be an independent body, since it had a special cult from which strangers were excluded. Once formed, no new family could be admitted. Nor could two tribes merge into a single tribe; their religion was against it. But, just as several phratries united in a tribe, many tribes could join together, on the condition that the cult of each was respected. The day this alliance took place, the city was born.
It matters little to know the reason which prompted several neighboring tribes to unite. Perhaps the union was voluntary, perhaps it was imposed by the superior power of one tribe, or by the powerful will of one man. What is certain is that the bonds of the new association created yet another cult. The tribes which grouped together to form a city never failed to light a sacred fire and to give themselves a common religion.
Thus human society, in this race, did not grow larger in the manner of a circle which little by little grows bigger, by degrees. On the contrary, little groups, formed long beforehand, joined together. Many families formed the phratry, many phratries the tribe, many tribes the city. Family, phratry, tribe, and city are, moreover, perfectly similar societies, one born of the other through a series of federations.
We must also point out that as each of these different groups joined together, they did not lose either their individuality or their independence. Although many families were united in a phratry, each family remained set up as in the time of its isolation; nothing was changed in it, its cult, its priesthood, its property rights, or its internal justice. Curiae then united, but each one kept its cult, its reunions, its holidays, its head. From the tribe we move to the city, but the tribes were not dissolved for this, and each one continued to form a unit, almost as if the city did not exist.
Thus the city is a grouping of individuals: It is a confederation of many groups which were formed beforehand and which continued to exist. In the Attic orators one sees that each Athenian was part of four distinct societies at the same time: He was a member of a family, a phratry, a tribe, and a city. (Foustel de Coulanges, La Cité Antique, book 2, pp. 143-145 passim).
Plinio Corrêa de Oliveira, Nobility and Analogous Traditional Elites in the Allocutions of Pius XII: A Theme Illuminating American Social History (York, Penn.: The American Society for the Defense of Tradition, Family, and Property, 1993), Documents VII, pp. 498-499.