I highly suggest reading up on the history of Venice, it's such an informative topic for me in studying history. For example, the War of the Legue of Cambrai is one of the most fascinating and illuminating wars that no one really knows about... a world war before the first world war. The origins of diplomacy (and espionage) there along with the banking and monetery systems alone are worth the study!

The oath of the council of ten? "Jura, perjura, secretum prodere noli" Swear, foreswear, and reveal not the secret.