Lower down, on the outside of this mask of rock, are more ramparts, built there by man, from which infantry could sweep the front of the enemy were they to approach from the only point from which a land attack is possible. The other side of the Rock, that which faces the Mediterranean, is unfortified, except by the big guns on the very summit, for no man could scale it, and no ball yet made could shatter its front. To further protect the north from a land attack there is at the base of the Rock and below the ramparts a great moat, bridged by an apparently solid piece of masonry. This roadway, which leads to the north gate of the fortress--the one which is closed at six each night--is undermined, and at a word could be blown into pebbles, turning the moat into a great lake of water, and virtually changing the Rock of Gibraltar into an island. I never crossed this roadway without wondering whether the sentry underneath might not be lighting his pipe near the powder-magazine, and I generally reached the end of it at a gallop. [Illustration: A SPANISH SENTRY] There is still another protection to the North Front. It is only the protection which a watch-dog gives at night; but a watch-dog is most important. He gives you time to sound your burglar-alarm and to get a pistol from under your pillow. A line of sentries pace the Neutral Ground, and have paced it for nearly two hundred years. Their sentry-boxes dot the half-mile of turf, and their red coats move backward and forward night and day, and any one who leaves the straight and narrow road crossing the Neutral Ground, and who comes too near, passes a dead-line and is shot. Facing them, a half-mile off, are the white adobe sentry-boxes of Spain and another row of sentries, wearing long blue coats and queer little shakos, and smoking cigarettes. And so the two great powers watch each other unceasingly across the half-mile of turf, and say, "So far shall you go, and no farther; this belongs to me." There is nothing more significant than these two rows of sentries; you notice it whenever you cross the Neutral Ground for a ride in Spain. First you see the English sentry, rather short and very young, but very clean and rigid, and scowling fiercely over the chin strap of his big white helmet. His shoulder-straps shine with pipe-clay and his boots with blacking, and his arms are burnished and oily. Taken alone, he is a little atom, a molecule; but he is complete in himself, with his food and lodging on his back, and his arms ready to his hand. He is one of a great system that obtains from India to Nova Scotia, and from Bermuda to Africa and Australia; and he shows that he knows this in the way in which he holds up his chin and kicks out his legs as he tramps back and forward guarding the big rock at his back. And facing him, half a mile away, you will see a tall handsome man seated on a stone, with the tails of his long coat wrapped warmly around his legs, and with his gun