The fortifications beside the Sea of Marmora were not called to occupy a prominent place in the active defence of the city; that is to say, they were never the object of a serious hostile attack. This was only what might be expected so long as the Empire maintained its naval superiority to the enemies with whom it was called to contend. But the Empire was not always master of the sea. And the immunity of these fortifications from attack was then due to the difficulties which the currents that sweep along this shore place in the way of the approach of ships within striking distance. The fear that the currents would carry his ships out to sea was the reason why Dandolo refused to bring the fleet of the Fourth Crusade into action against this side of the capital. The nearest semblance of an attack upon these fortifications was when Heraclius, in 610, brought up a fleet from Carthage to depose the tyrant Phocas, and took up a position before the Harbour of Julian or Sophia, the remains of which are seen in the quarter of Kadriga Limani below the Hippodrome. But that was more in the nature of a hostile demonstration than an active assault, for the citizens welcomed Heraclius as a deliverer, and carried Phocas to him as a prisoner. Still the comparative security of these walls from attack did not warrant leaving them in a state to tempt an enemy to strike a blow, and accordingly, though sometimes neglected in time of peace, they were promptly put in order whenever a hostile fleet was expected. This was particularly the case during the period of the Palæologi, when Genoa and Venice and the Ottoman Turks ruled on the sea, and the naval strength of the Empire had fallen into utter decay. In the siege of 1453, the Turkish fleet blockaded this side of the city from the Seraglio Point to Vlanga.