Eternity rings are traditionally given when a couple have been married for one year (not for an eternity & many men try to claim!) or after a couple have their first child
together. Nowadays traditions are changing though & what used to be an eternity ring design (a row of diamonds) is often worn as wedding ring. This means when the eternity ring is purchased there is often a nice symmetry created with the 2 rings sitting either side of the engagement ring.