The two forts which constituted the principal defenses of New Orleans against a naval attack from the sea were at Plaquemine Bend, about twenty miles above the Head of the Passes; by which name is known the point where the main stream of the Mississippi divides into several channels, called passes, through which its waters find their way to the Gulf. The river, whose general course below New Orleans is southeast, turns at Plaquemine Bend northeast for a mile and three-quarters, and then resumes its previous direction. The heavier of the two works, Fort Jackson, is on the right bank, at the lower angle of the Bend. It was a casemated brick structure, pentagonal in form, carrying in barbette over the casemates twenty-seven cannon of and above the size of thirty-two pounders, besides eleven twenty-four pounders. In the casemates were fourteen of the latter caliber. Attached to this fort, but below it, was a water battery carrying half a dozen heavy cannon. Fort St. Philip was nearly opposite Fort Jackson, but somewhat below it, so as to command not only the stream in its front, but also the stretch down the river, being thus enabled to rake vessels approaching from below before they came abreast. It comprised the fort proper and two water batteries, which together mounted forty-two guns. The sites of these fortifications had been skillfully chosen; but their armaments, though formidable and greatly superior to those of the fleet--regard being had to the commonly accepted maxim that a gun ashore is equivalent to four afloat--were not equal to the demands of the situation or to the importance of New Orleans. Out of a total of one hundred and nine pieces,[G] of which probably over ninety could be used against a passing fleet, fifty-six, or more than half, were of the very old and obsolete caliber of twenty-four pounders. [Footnote G: There were some guns bearing inland and some flanking howitzers, besides those already enumerated.]