Tiburtine Sibyl

She replied by showing him a vision of a young woman with a baby boy, high in the sky, while a voice from the heavens said "This is the virgin who shall conceive the saviour of the world", who would eclipse all the Roman gods.

The episode was regarded as a prefiguration of the Biblical Magi's visit to the new-born Jesus and connected Ancient and Christian Rome, implying foreknowledge of the coming of Christ by the greatest of Roman emperors.

It proved a useful rhetorical tool, valuable for many a ruler; the lists it contained of emperors and kings were revised to fit the circumstances, and hundreds of versions remain from the Middle Ages.

[5] Its conclusion purports to prophesy the advent in the world's ninth age of a final Emperor vanquishing the foes of Christianity (heavily dependent on the Apocalypse of Pseudo-Methodius): Then will arise a king of the Greeks whose name is Constans.

He will be tall of stature, of handsome appearance with shining face, and well put together in all parts of his body...This Emperor's reign is characterized by great wealth, victory over the foes of Christianity, an end of paganism and the conversion of the Jews.

Rogier van der Weyden , wing of the Bladelin Altarpiece , c. 1450
The Tiburtine Sibyl meets Augustus , Master of the Tiburtine Sibyl , Städelsches Kunstinstitut, Frankfurt .
The opening lines of Proffwydoliaeth Sibli Ddoeth . Tiburtine Sibyl was adapted in Welsh in the 13th century and preserved within Llyfr Coch Hergest at Jesus College, Oxford MS 111 (1385-1420)