Its origin is ascribed to the Germans, but the institution was probably far more ancient.

We find it forbidden[158] in the oldest code of laws in existence; and hence the _eric_ must have been in being at an early period of the world's civil history.
The law of succession, called _tanaisteacht_, or tanistry, is one of the most peculiar of the Brehon laws.

The eldest son succeeded the father to the exclusion of all collateral claimants, unless he was disqualified by deformity, imbecility, or crime.

In after ages, by a compact between parents or mutual agreement, the succession was sometimes made alternate in two or more families.

The eldest son, being recognized as presumptive heir, was denominated _tanaiste_, that is, minor or second; while the other sons, or persons eligible in case of failure, were termed _righdhamhua_, which literally means king-material, or king-makings.