These attacks, however, appear to have been chiefly intended as diversions, in order to hinder the enemy from obstructing the completion of the counter-wall. Now was the time for Nikias to adopt vigorous aggressive measures both against this wall and against the Syracusans in the field, unless he chose to relinquish all hope of ever being able to beleaguer Syracuse. And, indeed, he seems actually to have relinquished such hope, even thus early after he had seemed certain master of the city. For he now undertook a measure altogether new; highly important in itself, but indicating an altered scheme of policy. He resolved to fortify Cape Plemmyrium,—the rocky promontory which forms one extremity of the narrow entrance of the Great Harbor, immediately south of the point of Ortygia,—and to make it a secure main station for the fleet and stores. The fleet had been hitherto stationed in close neighborhood of the land-force, in a fortified position at the extremity of the double blockading wall between the southern cliff of Epipolæ and the Great Harbor. From such a station in the interior of the harbor, it was difficult for the Athenian triremes to perform the duties incumbent on them, of watching the two ports of Syracuse—one on each side of the isthmus which joins Ortygia to the mainland—so as to prevent any exit of ships from within, or ingress of ships from without, and of insuring the unobstructed admission by sea of supplies for their own army. For both these purposes, the station of Plemmyrium was far more convenient; and Nikias now saw that henceforward his operations would be for the most part maritime. Without confessing it openly, he thus practically acknowledged that the superiority of land-force had passed to the side of his opponents, and that a successful prosecution of the blockade had become impossible.[397] [397] Thucyd. vii, 4.