The Latin phrase in saecula saeculorum expresses the idea of eternity. It is biblical, taken from the Vulgate translation of the New Testament, rendering Greek εἰς τοὺς αἰῶνας τῶν αἰώνων. The usual English translation is "for ever and ever", but in Ephesians 3:21, the KJV notably has "world without end". Neither translation is literal, as the time span invoked is not literally eternity but an aiōn in Greek, translated as saeculum in Latin, and elevated to "an aiōn of aiōnes" or "a saeculum of saecula". The saeculum in Roman antiquity was the potential maximal human lifespan, or roughly a century. The original meaning of aiōn was comparable, and it is so used in Homer and Hesiod.
Some alternative English translations aim at greater literalness in their rendition of Ephesians 3:21: Young's Literal Translation and the Darby Translation have "of the age of the ages", Webster's Revision has "throughout all ages" while the New Living Translation has "through endless ages". In many modern English-language translations of eastern orthodox texts, such as the Divine Liturgy of St. John Chrysostom the phrase is often translated as 'unto ages of ages' .
The phrase occurs twelve times in the Book of Revelation alone, and another seven times in epistles, but not in the gospels:
It is taken up in medieval Christian liturgy, such as in the Tantum Ergo by Thomas Aquinas, in Veni Creator Spiritus, Gloria Patri and numerous other instances. When it is followed by an Amen, the last two words (saeculorum, Amen) may be abbreviated Euouae in medieval musical notation.
It does not occur in the Old Testament, which has other expressions for eternity, in Latin in aeternum et ultra "for eternity and beyond", rendering the Hebrew עד עולם, LXX εἰς τὸν αἰῶνα καὶ ἐπέκεινα, in English Bible translations usually also given as "for ever and ever".