Heh, I just played as the Getai myself and I think I know what your problem might be. Have you sacked Rome yet? It's not darkened on the map, but if you press the question mark to find your objectives, you'll notice that it's included in the list of raiding targets.

I kand of wish that it was darkened on the map for convenience too.

There are some other raiding targets you have that aren't on the victory conditions map.