In a long letter to the king, Cavour gave a detailed but probably not a complete account of the interviews at Plombières. It is said that among his papers, which Ricasoli, his successor in the premiership, gave to his heirs, but which they ultimately restored to the State, there is only one sealed packet--that which relates to this visit. He went by no means certain that the Emperor meant to do anything at all; he came away with great hopes, but still without certainty, for his trust in his partner was limited. He never felt sure whether Napoleon was not indulging on a large scale in the sport of building castles in the air, to which all semi-romantic temperaments are addicted. Still the basis of what bore every appearance of a definite understanding had been established. A rising in Massa and Carrara was to serve as the pretext of war. The object of the war was the expulsion of the Austrians from Italy, to be followed by the formation of a kingdom of Upper Italy, which should include the valley of the Po, the Legations, and the Marches of Ancona. Savoy was to be ceded to France. The fate of Nice was left undecided. To all of these propositions the king had authorised Cavour to agree. The hand of the Princess Clotilde was only to be conceded if it was made a condition of the alliance, which was not the case. Cavour believed, however, that everything depended on gratifying the Emperor's wish, and he strongly urged the king to yield a point which seemed to him of no great importance. Since most princesses made unhappy marriages, what did it matter if Prince Napoleon was a promising bridegroom or not? Victor Emmanuel was persuaded by the "reason of State"; but the sacrifice of his daughter cost him more than Cavour could ever conceive.
Napoleon told his visitor that he felt sure of the benevolent attitude of Russia, and of the neutrality of England and Prussia, but he had no illusions as to the difficulty of the task. The Austrians would be hard to crush, and unless thoroughly crushed they would not relax their hold on Italy. Peace must be imposed at Vienna. To this end at least 200,000 Frenchmen and 100,000 Italians would be necessary. Cavour has been criticised for acquiescing in the crippled programme of a kingdom of Upper Italy. What was he to do? Victor Amadeus II, in his instructions to the Marquis del Borgo, his minister at the Congress of Utrecht, laid down the rule: "Aller au solide et au présent et parler ensuite des chimères agréables." This was the only rule which Victor Emmanuel's minister could observe with any profit to his country at Plombières. As he wrote himself, "In politics one can only do one thing at a time, and the only thing we have to think of is how to get the Austrians out of Italy."