At one place, in looking over the parapet of such a bridge, you see a vast market, with carts filled with vegetables standing all around it. At another, you behold a great railway station, with crowds of passengers on the platforms, and trains of cars coming and going; at another, a range of beautiful gardens and pleasure grounds, with ladies and gentlemen walking in them, or sitting on seats under the trees, and children trundling their hoops, or rolling their balls, over the smooth gravel walks. Sometimes a street of the upper town, running along on the crest or side of a hill, lies _parallel_ with one in the lower town, that extends below it in the valley. In this case the block of houses that comes between will be very high indeed on the side towards the lower street; so that you see buildings sometimes eight or ten stories high at one front, and only four or five on the other. These structures consist, in fact, of two houses, one on top of the other; the entrances to the lower house being from one of the streets of the lower town, and those leading to the one on the top being from a street in the upper town. The reason why Edinburgh was built in this extraordinary position was, because it had its origin in a castle on a rock. This rock, with the castle that crowns the summit of it, rears its lofty head now in the very centre of the town, with deep valleys all around it. This rock, or rather rocky hill,--for it is nearly a mile in circumference,--is very steep on all sides but one. On that side there is a gradual slope, a mile or more in length, leading down to the level country. A great many centuries ago the military chieftains of those days built the castle on the hill. About the same time the monks built a monastery on the level ground at the foot of the long slope leading down from the castle. The rocky hill was an excellent place for the castle, for there was a hundred feet of almost perpendicular precipice on all sides but one, and on that side there was a convenient slope for the people who lived in the castle to go up and down; and thus, by fortifying this side, and making slight walls on all the other sides, the whole place would be very secure. The level ground below, too, was a very good place for the monastery or abbey; for it was easily accessible from all the country around, and was, moreover, in the midst of a region of fertile land, easy for the lay brethren to till. There was no necessity that the abbey should be in a fortified place, for such establishments were considered sacred in those days, and even in the most furious wars they were seldom molested.