Renaissance Italy surely is famous for banking/trading and for the patronage of the arts and the many architectural beauties but what about a military twist to the civ? There have been plenty of "Italian wars" and plenty of innovations in miltiary affairs came out of Italy at the time, some ability based around mercenaries and medieval/renaissance war would make sense as well.
A unique fort improvement with ZOC and a weak one tile ranged attack (with the due limitations in positioning to avoid making it broken) would be a nice reference to the military revolution of the early modern period and the innovation of Italian forts. A unique unit based around mercenaries would not be bad either, perhaps the Italian fort could replace the encampment and reduce maintenance for units or make them cheaper to buy? Would work nicely as a combo with bonuses from a unique commercial district/building.