The text evidently enjoyed some popularity, since there are over seventy manuscripts of the long recension. The author belonged to the Romani party and used the Paschal cycle of Victorius of Aquitaine. His explanation of the sun and moon standing still at the command of Joshua (Josh. 10: 12–13) includes a dating clause stating that he was writing in the third year of the twelfth 532-year cycle since the creation of the world, which dates the text quite precisely to 655; this passage is also quoted in an eighth-century Irish computus (Munich, Bayerische Staatsbibl., Clm 14456 (Regensburg)). The Irish provenance of the text is known from internal references to the death (652) of Manchán of Min Droichit (Manchán (qv) of Liath Mancháin) and other Irish savants, and from references to Irish fauna and tidal data. The latter would indicate that he was writing in a monastery in the south-west. He styles himself Augustinus in his dedication (I, 4), which he addresses to ‘the venerable bishops and priests of the cities and monasteries, most especially of the Carthaginenses’. The final phrase has recently been interpreted as referring not to ‘the city of Carthach’ (qv), that is Lismore, but to Inis Cathaig (Scattery Island), the foundation of St Senan (qv) in the Shannon estuary, taking Carthaginenses to be a corruption of Cathagenses. He states that he was commissioned to write the ‘De mirabilibus’ by his spiritual mentor Eusebius, who has not been identified with any certainty. The work, along with that of the author of the seventh-century ‘De ordine creaturarum’, gives us a rare insight into the cosmological understanding of a medieval Irish savant.