Once you control 3 out of 5 seats, you can purchase the "City Key." This allows you to take over the entire island instantly without firing a single shot.
With the addition of new ornaments and the system, city planning becomes even more vital. Anno 1404 Venice Guide
to access Venetian ship blueprints.
Cause riots that stop production and damage buildings. Once you control 3 out of 5 seats,
A floating fortress of commerce. It has more hit points than a standard Large Trading Ship and massive cargo slots, making it the king of long-distance Orient-to-Occident routes. 5. Efficient City Layouts for Venice Anno 1404 Venice Guide