Spanish crisis. This article proposes to point out the importance of the Genoese 17th century network in information and negotiation: it was a rich grounds for diplomatic manoeuvres carried out in both formal and informal ways. The Duke of Modena Francesco d’Este, one of the most active Italian princes, performed a small "diplomatic revolution" in the 1640’s, shifting from the Spanish to the French field. This reversal is reflected in the Genoese scene, where the Duke breaks his ties with the Grimaldi de Castro family - previously used to strengthen his relationship with Madrid - to establish contact with a Genoese patrician close to the French court, Giannettino Giustiniani. A risky move, although supported by the Genoese Cardinal Girolamo Grimaldi. Genoa watched these movements with cautious interest, trying to obtain greater profits from the serious crisis of Spanish power. This non-committal attitude highlights the important geo-political, as well as financial, role played by the Republic of Genoa and its oligarchy.
Keywords: Republic of Genoa, Duchy of Modena, Giannettino Giustiniani, informal diplomacy in the 17th century, the role of Genoa in international balances, the military attack of Mazzarino in Italy