Postumius Rufius Festus Avienius (or Avienus) was a Latin writer of the 4th century AD. He was a native of Volsinii in Etruria, from the distinguished family of the Rufii Festi.

Avienius is not identical with the historian Festus.

Avienius made a free translation into Latin of Aratus' didactic poem Phaenomena. He also took a popular Greek poem in hexameters, Periegesis, briefly delimiting the habitable world from the perspective of Alexandria, written by Dionysius Periegetes in a terse and elegant style that was easy to memorize for students, and translated it into an archaising Latin as his Descriptio orbis terrae ("Description of the World's Lands"). Only Book I survives, with an unsteady grasp of actual geography and some far-fetched etymologies: see Ophiussa.

He wrote Ora Maritima, a poem claimed to contain borrowings from the 6th-century BC Massiliote Periplus. Avienius also served as governor of Achaia and Africa.

According to legend, when asked what he did in the country, he answered Prandeo, poto, cano, ludo, lavo, caeno,^{[check spelling]} quiesco:

I dine, drink, sing, play, bathe, sup, rest.

However this quote is a misattribution and likely comes from the works of Martial.