FORTIFICATIONS erected under the trained skill of cultivated military engineers have long been the chief means of defence for all civilized cities and countries. It is therefore a little remarkable, that while New York was from the earliest settlement the chief city and heart of the country, no general effort to suitably fortify its approaches was made until the outburst of the war of 1812.

Rude fortifications were then placed upon some of the small islands, in the upper bay, and Fort Lafayette was commenced on Hendricks Reef, 200 yards from the shore, in what is known as the Narrows, the water doorway to the Metropolis. This fort, when completed, had cost about $350,000, and mounted seventy-three heavy guns. Its chief fame during the half-century has arisen from the fact of its having been made the house of detention for political prisoners during the late civil war, and some who read this notice will require no fuller description of it. The elements were unfriendly to this fortress, however, and on the first of December, 1868, it was destroyed by fire, leaving only the naked walls. The government is about to rebuild it on a greatly improved scale.

In 1824, Fort Hamilton was commenced, immediately opposite the former, standing on an eminence on the Long Island shore. It was completed in 1832, at an expense of $550,000, and mounted sixty heavy guns. It has recently been supplemented with a strong battery, and now numbers in its armament some of the celebrated Rodman guns, that discharge a spherical ball weighing a thousand pounds. Several of the other guns throw balls weighing four hundred and fifty pounds. Directly opposite these works, on the Staten Island shore, stand Forts Richmond and Tompkins, both new and improved works, constructed of gray stone, mounting many guns of huge calibre. Fort Tompkins is a water battery of formidable appearance, while Fort Richmond occupies the bluff in its rear, spreading out with its accompanying batteries at great length, and is so arranged as to shoot over Fort Tompkins, and sweep the channel for miles. Batteries Hudson, Morton, North Cliff, and South Cliff have been completed, and another is now being constructed. The channel at this point is but little more than a mile wide, and these fortifications are so arranged that with suitable projectiles and management, such a shower of balls and shells may be rained as to prevent the entrance of a fleet of iron-clads.

The upper bay is favored with several islands, admirably arranged for fortifications. Ellis Island, two thousand and fifty yards southwest from, Castle Garden, is occupied by Ford Gibson, built in 1841-44, mounting fifteen or twenty guns, and requiring a garrison of one hundred men. Bedloe's Island, situated 2,950 yards southwest of Castle Garden, is occupied by Fort Wood, erected in 1841, at a cost of $213,000, on the site of a fort built at the beginning of the century. It has space for eighty guns, and a garrison of three hundred and fifty men. A strong battery is now being added to this fort.

Governor's Island containing seventy-two acres, and situated ten hundred and sixty-six yards from Castle Garden, is also wholly devoted to maritime defence. Its largest work is Fort Columbus, a star-shaped fortification with five points, standing on the summit of the island, with quarters for many troops. Castle William is a three-story round tower, situated on the west shore of the island, six hundred feet in circumference, and sixty feet high, mounting over one hundred guns. South Battery fronts on Buttermilk channel, separating the island from Brooklyn (which channel was once forded by cattle, but now affords anchorage for heavy ships), and mounts fifteen heavy guns. An immense barbette battery is now being constructed on this island, which will require several years for its completion. Governor's Island, in time of war, requires a garrison of a thousand men. Acres of its surface are covered with heavy cannon, and with pyramids of balls and shells, thoroughly painted to resist the action of the elements. Here recruits are drilled for the service, and deserters detained as prisoners. There are also very extensive works at Sandy Hook, New Jersey, calculated to prevent the occupation of the lower bay, as a place of anchorage to an enemy's fleet.

Fort Schuyler, a large strong fortification, constructed of gray stone, mounting over three hundred guns, and requiring a war garrison of fifteen hundred troops, stands at Throggs Neck, several miles up the East river, and is designed to prevent the approach of armed vessels to New York by way of Long Island Sound. This fortification is being extensively remodelled, at an expense of several hundred thousand dollars. Willet Point unites with Fort Schuyler in guarding this eastern channel of approach, which, with the late improvements at Hurl Gate, requires to be more carefully defended than formerly. Willet Point is the principal engineer depot of the department of the East. Here the surplus stores which accumulated during the war were largely deposited. Here bridge-trains, and equipage, intrenching, mining, and other tools, are preserved for use, in future field service. The depot is guarded and cared for, and the property issued by engineer troops. This place is also, at present, the Torpedo, School of the United States army, and extensive experiments in that line are now being made. Many millions have been consumed on these fortifications and their armament, which cover all the strong points about the harbors, and vast sums, are still being expended; yet, with all this, it is doubtless true that New York is not defended as its importance demands. The old walls, guns, and round shot of the fathers are of little use in these days of improved projectiles and floating batteries. And while we would not encourage a useless expenditure in the arts of war, too much pains can scarcely be taken by the government to prevent the capture of the Metropolis, in the event of a sudden conflict with a maritime power. It should also be remembered that while the nations are beating their ploughshares into swords, and their pruning hooks into cannon and shells, to thoroughly prepare for war is the surest promise of peace.