Avienus' version of Aratos' didatic poem 'Phainomena', written around AD 360, is notorious for its difficulty. Reworking earlier didactic literature, Avienus extended or shortened the original versions as he pleased. This commentary includes detailed information on astronomical history and the mythology of the constellations; it tries to explain both the poet's technique and his often baroque text. Avienus has an individual approach to the use of epic formulae and literature sources. The analysis makes very clear that this pagan writer is an underestimated poeta doctus of an era in which Christianity hat long been dominant.