[Illustration: THE NEW MOLE AND ROSIA BAY.]
Within the Line-Wall, immediately fronting the bay, are the casemates and barracks for the artillery regiments that are to serve the guns. The casemates are designed to be absolutely bomb-proof, the walls being of such thickness as to resist the impact of shot weighing hundreds of pounds, while the enormous arches overhead are made to withstand the weight and the explosion of the heaviest shells. Such at least was the design of the military engineers who constructed them: though, with the new inventions in war, the monster guns and the new explosives, it is hard to put any limit to man's power of destruction. This Line-Wall is armed with guns of the largest calibre, some of which are mounted on the parapet above, but the greater part are in the casemates below, and therefore nearer the level of the sea, so that they can be fired but a few feet above the water, and thus strike ships in the most vital part.
The latest pets of Gibraltar are a pair of twins--two guns, each of which weighs a hundred tons! These are guarded with great care from the too close inspection of strangers. No description can give a clear impression of their enormous size. In the early history of artillery, the Turks cast some of the largest pieces in the world. Those who have visited the East, may remember the huge cannon-balls of stone, that may still be seen lying under the walls of the Round Towers on the Bosphorus. But those were pebbles compared with shot that can only be lifted to the mouth of the guns by machinery. The bore of these monsters would delight the soul of the Grand Turk, for, (as a man could easily crawl into one of them,) if the barbarous punishment of the old days were still reserved for great offenders, a Pasha who had displeased the Sultan might easily be put in along with the cartridge, and be rammed down and fired off!
The guns had recently been tried, and found to be perfect, though the explosion was not so terrible as had at first been feared. There had been some apprehension that a weapon which was to be so destructive to enemies, might not be an innocent toy to those who fired it; that it might split the ear-drums of the gunners themselves. Some years ago I was at Syra, in the Greek Archipelago, when the English ironclad Devastation was lying in port, which had four thirty-five-ton guns, (the monsters of that day,) and one of her officers said that they "never fired them except at sea, for that the discharge in the harbor would break every window in the town." But here the effect seems not to have been so great. One who was present at the firing of one of the hundred-ton guns, told me that all who stood round expected to be deafened by the concussion. Yet when it came, they turned and looked at each other with a mixture of surprise and disappointment. The sound was not in proportion to the size. Indeed our Consul tells me that some of the sixty-eight pounders are as ear-splitting as the hundred-ton guns. But an English gentleman whom I met at Naples gave me a different report of his experience. He had just come from Malta, where they have a hundred-ton gun mounted on the ramparts. One day, while at dinner in the hotel, they heard a crash, at which all started from their seats, and rushed to the windows to throw them open, lest a second discharge should leave not a pane of glass unbroken. But this came only as they left the harbor. When about three miles at sea, they saw the flash, which was followed by a boom such as they never heard before. It was the most awful thunder rolling over the deep in billows, like waves of the sea, filling the whole horizon with the vast, tremendous sound. It was as "the voice of God upon the waters."