Still, there was to be a Prussia. Between the two great empires was to lie, in realization of a long-cherished plan, a girdle of neutral states like the "marches" established by Charles the Great. In this line Silesia was the only break. Prussia and Austria, one on each side of this mark, shorn of their strength and prestige, might await their destiny. France was to mediate for peace between Russia and Turkey, Russia between England and France. In case Great Britain should not prove tractable,--that is, admit the sanctity of all flags on the high seas, and restore all the colonies of France and her allies captured since 1805,--then Russia, in common with France, Denmark, Sweden, Portugal, and Austria, would declare commercial war on England, and complete the continental embargo on British trade. Should Turkey refuse favorable terms, the two empires would divide between them all her European lands except Rumelia and the district of Constantinople. Alexander afterward declared that Napoleon gave a verbal promise that Russia should have a substantial increment on the Danube. The rumor was that Bessarabia, Moldavia, Wallachia, and Bulgaria were indicated to the Czar as his share. No mention was made of Austria, which the treaty of Presburg had sufficiently dismembered. But Prussia? In order to complete the great "march" between east and west, Silesia was essential. At first Napoleon thought of combining it with Prussian Poland to form a kingdom. This would not restore the real Poland, but it would create a Poland, and give him a Polish army. It was already decided that the Elbe should form Frederick William's western frontier; to weaken his strength still further would destroy all balance between Prussia and Austria. Moreover, Alexander made a tender appeal, and adroitly suggested a distasteful counter-proposition. Accordingly it was settled that the great province should remain Prussian. This was a large concession to the Czar.