The question of the demolition of the barrier fortresses had been proceeding side by side with the settlement of the conditions under which Belgium was to be separated from Holland. Talleyrand, however, was not admitted to these negotiations which were conducted between the plenipotentiaries of Great Britain, Austria, Russia and Prussia and those of Belgium. The result of their deliberations was embodied in a document, known as the Fortress Convention, which was signed by the representatives of the five Powers concerned on December 14, 1831. When La Tour-Maubourg had been sent to Brussels, during the French occupation of Belgium, he had been instructed to press for the demolition of the fortifications of Ath, Mons, Menin, Charleroi and Tournay. The Powers, however, elected to preserve the defences of the two last-named towns and to dismantle in their place the works of Philippeville and Marienburg. Palmerston, without doubt, was mainly responsible for this decision which was to create great dissatisfaction in Paris. He was resolved, under no circumstance, to admit the principle of allowing France to have a voice in determining which of the fortresses, erected at the expense of the four Powers, should be destroyed. After her attempts to arrive at a separate understanding with Belgium concerning them, he may have thought that she required to be reminded of the true state of the case. Yet it would appear that the mere fact that her plenipotentiary had not appended his signature to the convention must have made her position in the matter sufficiently clear to the world. But, in persuading the members of the conference to substitute Philippeville and Marienburg for Charleroi and Tournay, Palmerston was not actuated by a desire wantonly to slight France. In the question of the destruction of the Belgian fortresses Grey's Cabinet was in a very delicate position as regards the Parliament.[174] An embittered opposition was bound to demand to know on what grounds the government proposed to justify its policy of sanctioning the demolition of fortifications, which the greatest captain of the day had pronounced to be necessary to the security of Europe. Now Wellington, it would appear, considered Charleroi and Tournay as of more importance to the defence of Belgium than Philippeville and Marienburg, and Lord Grey and his colleagues could not afford to disregard his opinion. It must be remembered also that, on several occasions during the course of the negotiations, France had shown a strong desire to regain possession of these two places of which she had been deprived after Waterloo, and it was hoped that, were their fortifications to be demolished, they would cease to offer the same attractions to her.[175]