Commentary

• Romae: Remember CitSiDHR — cities, small islands, domus, humus, and rus — often appear in the locative case, which denotes place where without the use of a preposition. Loc
quantus ... bellis: Understand that fuerat belongs in this clause and make quantus the subject. Translate as "However great it had scarcely been during the time of Hannibal (and) the Punic Wars..."
Hannibalis ... bellis: Hannibalis tempore and Punicis bellis are used together as ablatives to denote time when, i.e., 218-201 BCE. AblTime

Hannibal (Barca) was a successful Carthiginian military commander during the Second Punic War. This was a war between the Roman forces and the Carthiginian forces in North Africa over control of the Mediterranean. He successfully marched his army from Iberia (modern day Spain) through the Pyrenees mountain range and into Italy. He had three very successful victories over the Romans at Trebia, Trasimene, and Cannae. Each of these battles were equally as devestating to the Roman forces as the German victory at Arausio near the Rhone river (Brev. V.1.1) For a map of his routes and these key battles, see here.
ne...venirent: A negative result clause signalled by the quantus, the ne, and the imperfect subjunctive, venirent. This clause demonstrates the effect of the Romans' great fear. UtRes.
Romam: Remember that CitSiDHR nouns, while not using a pronoun to show place where, also does not rely on the preposition ad to denote place to which. Loc