Venetian Heavy Infantry

[Chaotix]

You pretty much need a citadel (Lv. 5 castle) with a barracks (Lv. 5 inf. recruitment) before you can recruit Venetian Heavy Infantry, so you'll be well into your campaign before you recruit them. Before you can get them, though, a mix of Italian Spear Militia, and some Dismounted Feudal Knights once you get good castle ready, is all that you'll really need. Don't overlook the Venetian Archers either- heavy armored missile troops.

Hold on, I'll check my completed Venice campaign and let you know exactly what level.

EDIT: I was wrong, you only need a fortress, and the barrack is only a tier 4 building. Still won't be seeing them for a while, considering slow castle growth + troop recruitment detracting from population