Stirpes (Roman clan)

A stirpes is a branch of a Roman Gens, marked by a cognomen (epiphet). Since about the 2nd century BC, Roman clans usually distinguished the branches differing from the main house with differing cognomina. Gentes without official stirpes or low rank thus have no cognomina. While originally the clans made no high distinction between its branches, the rise of the number of people called Iulia Caesar during the 1st century AD made it necessary to register official branches in the Imperium, especially for the various high clans and mage clans, with the corresponding cognomina.

Example
The Gens Tullia, a Volscian-Roman Mage clan of Republican origin, recognises three stirpes including the main family. It thus has three cognomina: Members of the main line are called Cicero, and the two side houses are Severus (which in modern times runs the Tullian Mage school) and the Insitor.