Two months were spent by him in conferences and diplomacy. From the 9th to the 20th of July, 1806, he was engaged with the Russian plenipotentiary, and their interviews were terminated by the wonderful treaty which opened and ceded to France, Cattaro, a Venetian territory in Dalmatia, with its capital, harbour, and citadel; and which maintained Gustavus IV. in possession of the ancient Duchy of Pomerania, and left to be achieved, at an early period, the junction of Sicily to the kingdom of Murat--the whole being arranged by them, without condescending to ask the advice of Great Britain, which was then the faithful ally of Prussia. This treaty was never ratified by the Emperor Alexander. The other conferences took place between Clarke and Lord Yarmouth, to whom Charles Fox added the Scottish Earl of Lauderdale; while, to assist Clarke, the French government added Jean Baptiste Champagny, the Duc de Cadore, who was only a spectator of the negotiations, which were without result, and are of no consequence to the reader; but Clarke, who had displayed his usual acuteness, tact, and skill in all his meetings with the Lords Yarmouth and Lauderdale, was not a little proud of having prevailed upon M. D'Oubril to sign certain clauses he submitted to him. Russia, however, was in no haste to evacuate Cattaro, and the Emperor Alexander began to augment his army; so from September, 1806, it became evident that if France declared war against Prussia, she would have to encounter Russia also. In the first meeting concerning these affairs Clarke said, "that the convention recently concluded with Russia was for France equivalent to a victory; and that henceforward his master, the Emperor Napoleon, had the right of proposing articles more advantageous than those he had lately made." He qualified the terms of the treaty which he wished them to adopt, and in particular _l'uti possedetis_; of vague conversations on the politics of Rome, he said that Bonaparte had never adopted this _uti possedetis_ for a basis, without which Moravia, Styria, and Carniola would have remained still in his hands. Similar language, encumbered by diplomatic technicalities, was applied to the two envoys of Fox, but failed to succeed with them, as they were resolved not to depart in a single instance from the basis of the position taken before by the envoy of Prince Talleyrand. The death of Charles Fox put an end to all the hopes of peace, although Lauderdale and Champagny did not despair of procuring it until the 6th of October; but by this time Clarke had set out for Germany, having accompanied Napoleon to the Prussian campaign. After the two battles of the 14th October, he was named Governor of Erfurt, a fortified city on the Gera, and capital of the Elector of Mentz. It was then crowded with Prussian prisoners, and with sick and wounded Frenchmen.