The French alliance still rested on nothing more substantial than a secret unwritten engagement which Napoleon could repudiate at will. Cavour, who would have made an excellent lawyer, strove his utmost to obtain some more solid bond, for which the marriage-visit of Prince Napoleon offered a favourable opportunity. The connection with one of the oldest royal houses in Europe so flattered the Emperor's vanity that he authorised the bridegroom and General Niel, who accompanied him, to sign a treaty in black and white, binding France to come to the assistance of Piedmont, if that State were the object of an act of aggression on the part of Austria. Possibly, like other people, he thought that no such act of aggression would be made, and that he remained free to escape from the contract if he chose. A military convention was signed at the same time, one of the clauses of which Cavour was fully determined to have cancelled; it stipulated that volunteer corps were to be excluded. He signed the convention, but fought out the point afterwards and gained it, in spite of Napoleon's strenuous resistance. These transactions were intended to be kept absolutely secret, and the French ministers do not seem to have known of them, but somehow the European Courts, and Mazzini, got wind of a treaty having been signed. Different rumours went about: the Prince Consort was informed that Savoy was to go for Lombardy, and Nice for Venetia; others said that Nice was to be the price of the Duchies and Legations. There was a persistent impression that the island of Sardinia was mentioned, which would not merit record but for the general correctness of the other guesses. There is no reference, however, to Sardinia, in the version of the treaty which has since been published, and Cavour indignantly repudiated the idea of ceding this Italian island to France, when the charge of having entertained it was flung at him a year later. Some doubt may linger in the mind as to whether there was not a scheme for giving the Pope Sardinia in return for part or all his territory.