The Byzantine fleet, as Leo describes it, had for its chief object the maintenance of the police of the seas in the Aegean, Levant, and South Italian waters. Its enemies were the Saracens of the Syrian and African coasts, and more especially the troublesome Corsairs of Crete, who were often beaten but never subdued till Nicephorus Phocas exterminated them in 961. The empire maintained three fleets, small ones in the Black Sea and in Western waters; but the largest in the Aegean. This was composed of sixty “dromonds,” or war-vessels of the largest rating; their great depôt was in the arsenal at Constantinople, but they could also be refitted at Samos, Thessalonica, and several other ports. Owing to their superior size, and still more to their employment of the celebrated Greek fire, the imperial fleets generally had the better of the Saracen, but though they checked his larger squadrons, they could never suppress the petty piracy by isolated sea-robbers, which rendered all mediæval commerce so dangerous. The works of Constantine Porphyrogenitus are even more interesting than those of his father. His treatise called “On the Themes” is invaluable to the historian, as it gives a complete list of the Themes, their boundaries, inhabitants, characteristics, and resources, with some other incidental notices of value. Still more important is the book, “On the Administration of the Empire,” which contains directions for the foreign policy of the realm, and sketches the condition and resources of the various nations with whom the Constantinopolitan government had dealings. Constantine also wrote a biography of his grandfather, Basil the Macedonian, couched in terms of respect which that hardy usurper was far from deserving. But his longest and most ambitious work was on Court Ceremonies, a manual of etiquette and precedence, describing the official hierarchy of the empire, its duties and privileges, and containing elaborate directions for the conduct of state ceremonials and the interior economy of the royal household. On this comparatively trifling topic Constantine spent far more pains than on the works of larger interest which he composed. His books show him to have been a man of no great originative faculty, but gifted with the powers of a careful and methodical compiler, who loved details and never shirked trouble. His care for court pageants was very characteristic of the peaceful emperor, who had long been kept at home by his guardian, and forced to compensate himself by ceremonial for the want of real power.