post victoriam Iugurthinam:
After his victories in Numidia, Marius became very popular
with the Roman people. As the Cimbrian War dragged on,
Rome continued to place their trust in his military leadership and reelect him to the position of consul.
secundo:
Understand tempore with secundo. Marius was elected to the consulship
on seven different occasions — a highly irregular and unheard of occurence.
consul est factus:
After sum and verbs of becoming, making, naming, and appearing,
a predicative nominative is used rather than an accusative.
PredNom
bellumque ei ... decretum est:
As a compound verb, decretum est takes a dative object, ei, i.e., Marius.
DatComp
tertio...quarto:
Again, tempore is understood with each of these words as
Eutropius stresses the number of times Marius was made consul.