It was held after the Seventeenth Council in 694, probably in 703 during the reign of King Wittiza (701–710) or his co-reign with his father, Ergica, from 693.
An account of the acts of the council existed in the Middle Ages, but has since been lost; it may have been highly controversial, leading to its suppression.
[1] There is a reference in the Chronicle of 754 to Wittiza commanding Sindered to exert pressure on the established clergy, but what exactly this means is unknown.
[2] It may mean that he pressured the Eighteenth Council to ratify the decision of the Quinisext Council that clerical marriage was permissible: according to the Chronicle of Alfonso III, Fruela I of Asturias (757–68) reversed this ruling.
[3] The collective sense is that Wittiza made an effort to reform corruptions in the Visigothic Catholic Church.