359. Peculiar Genitive constructions are the following.
a. A poetical genitive occurs rarely in exclamations, in imitation of the Greek (Genitive of Exclamation).
Dī immortālēs, mercimōnī lepidī! (Pl. Most. 912)
Good heavens! what a charming bargain!
Foederis heu tacitī! (Prop. 4.7.21)
Alas for the unspoken agreement!
b. The genitive is often used with the ablatives causā, grātiā (for the sake of); ergō (because of); and the indeclinable īnstar (like); also with prīdiē (the day before) postrīdiē (the day after); tenus (as far as).
with due respect
(for the sake of honor)
êius lēgis ergō
on account of this law
equus īnstar montis (Aen. 2.15)
a horse huge as a mountain (the image of a mountain)
laterum tenus (id. 10.210)
as far as the sides
Note 1— Of these the genitive with causā is a development from the possessive genitive and resembles that in nōmen īnsāniae (§ 343.d). The others are of various origin.
Note 2— In prose of the Republican Period prīdiē and postrīdiē are thus used only in the expressions
prīdiē (postrīdiē) êius diēī
the day before (after) that
(cf. “the eve, the morrow of that day”)
Tacitus uses the construction with other words.
the day after the plot