His sole known work is the Prodigiorum liber (Book of Prodigies), a tabulation of the wonders and portents (prodigia) that had occurred in the Roman Republic and early Principate in the years 249–12 BC.
[1] The material for the Prodigiorum liber was largely excerpted from the 1st century AD Ab Urbe Condita Libri of the Augustan historian Livy, which chronicled the history of the Roman state from its origin to the beginning of the imperial period, though Julius used it selectively and sometimes added interpretations of the omens and incidents he included.
Of great importance was the edition by the Basle humanist Conrad Lycosthenes (1552), trying to reconstruct lost parts and illustrating the text with wood-cuts.
Later editions were printed by Johannes Schefferus (Amsterdam, 1679), Franciscus Oudendorp (Leiden, 1720) and Otto Jahn (1853, with the periochae of Livy).
The text of Julius Obsequens frequently makes reference to unusual astronomical and meteorological events as portentous signs like meteor showers, comets, and sun dogs, alongside earthquakes, aberrant births, haruspicy, and sweating, crying, or bleeding statues.