Due to their lack of political organization, throughout their long history the Celts failed to achieve any lasting territorial control.  They compensated for this by developing tightly knit, extended family units that gave them cohesion at grass roots level and formed the basis of the clan system.

The Celts operated on a tribal basis, holding their land in common and owing their principal allegiance to a chief.  Their basic territorial measurement was the tuath, or tribe, which was large enough to provide a fighting force of anything between 500 and 3,000 men.

The word "clann" in Gaelic means children of the family.  Each clan was a large group of related people, theoretically an extended family, supposedly descended from one progenitor and all owing allegiance to the chief as their head and their protector.  The clan also included those who married into the clan as well as other unrelated individuals who joined the clan for protection and support.

Historically clans were located predominantly in the Highlands and islands since that is where most of the Gaelic speaking peoples lived.  In the Lowlands and Border region (the area long the border with England) similar groups were known as families.  Nowadays many of these families have adopted the term "clan."


"Sept" is a term borrowed from Irish Culture in the nineteenth century to explain the use of a variety of surnames by members of a single clan.  In Ireland "sept" is roughly synonymous with the Scottish "clan" and refers to an intra-related or dependent family.  Where Scots would refer to "MacGregor and his clan" and Irish historian might say "O'Neill and his septs."  The Irish historically had princes and thought in terms of place rather than surname.  Thus, the surname "O'Brian" might be a sept of several different princes.  In Scotland, only in the case of larger clans with distinct and sometimes widely separated sub-families is the term "sept" appropriate.  The variety of surnames within a Scottish clan do not represent separate and definable sub-clans, but instead reflect the vagries of transition of the Gaels into the English naming system as well as marriages, migrations, and occupations.  The main family itself may have developed a variety of surnames.