The marquisate was fairly unimportant at the verge of the second millenium, so we decided to have a combined faction of Pisa/Tuscany. In fact, think of it more like a Pisan faction which recruits Tuscanian units from its hinterland.

We did this with a few factions who we felt wouldn't alone be strong enough to survive. Since we can't have every small city state represented and can't simulate the reasons why they existed or survived in the first place, this is a decent compromise.