Participation in the Crusades was not a solitary proof of the importance of the naval states of Italy. That they had been able to act effectively in the Levant may have been in some measure due to the weakening of the Mohammedans by the disintegration of the Seljukian power, the movements of the Moguls, and the confusion consequent on the rise of the Ottomans. However that may have been, the naval strength of those Italian states was great absolutely as well as relatively. Sismondi, speaking of Venice, Pisa, and Genoa, towards the end of the eleventh century, says 'these three cities had more vessels on the Mediterranean than the whole of Christendom besides.'[29] Dealing with a period two centuries later, he declares it 'difficult to comprehend how two simple cities could put to sea such prodigious fleets as those of Pisa and Genoa.' The difficulty disappears when we have Mahan's explanation. The maritime republics of Italy--like Athens and Rhodes in ancient, Catalonia in mediæval, and England and the Netherlands in more modern times--were 'peculiarly well fitted, by situation and resources, for the control of the sea by both war and commerce.' As far as the western Mediterranean was concerned, Genoa and Pisa had given early proofs of their maritime energy, and fixed themselves, in succession to the Saracens, in the Balearic Isles, Sardinia, and Corsica. Sea-power was the Themistoclean instrument with which they made a small state into a great one. [Footnote 29: _Ital._Republics_, English ed., p. 29.]