Iam deinde, tribūnīs mīlitāribus cōnsulārī imperiō rem pūblicam Rōmae regentibus, ad annum ferē conditae urbis trecentēsimum quadrāgēsimum septimum, trīgintā illī tyrannī praepositī sunt ā Lacedaemoniīs Athēniēnsibus, et in Siciliā Dionysius superior tyrannidem tenuit;
I’ve grown accustomed to seeing conditam Rōmam in Orberg’s selection from Aulus Gellius. Why is it here in the genitive conditae urbis?
It refers to annum. It’s the same as ab urbe condita.