text: 's two castles of Europe and Asia was made almost impregnable by the construction of the formidable line of sea defences still existing; the necessity for which had been demonstrated by the recent attack of the Venetians; and fortified posts were established along the line of the Dnieper and Dniester to keep in cheek the predatory Cossacks between these rivers who were at this time engaged in a furious civil contest with the king of Poland the ally of the Porte