6. Some mounds are considerably higher than the others and of a peculiar shape, almost like a pyramid, that is, ending in a point from which it slopes down rapidly on all sides. Such is the pyramidal mound of Nimrud, which Layard describes as being so striking and picturesque an object as you approach the ruins from any point of the plain.[J] Such also is the still more picturesque mound of BORSIP (now BIRS NIMRUD) near Babylon, the largest of this kind.[K] These mounds are the remains of peculiar constructions, called ZIGGURATS, composed of several platforms piled one on the other, each square in shape and somewhat smaller than the preceding one; the topmost platform supported a temple or sanctuary, which by these means was raised far above the dwellings of men, a constant reminder not less eloquent than the exhortation in some of our religious services: "Lift up your hearts!" Of these heavenward pointing towers, which were also used as observatories by the Chaldeans, great lovers of the starry heavens, that of Borsip, once composed of seven stages, is the loftiest; it measures over 150 feet in perpendicular height. [Illustration: 11.--MOUND OF MUGHEIR (ANCIENT UR).] 7. It is evident that these artificial hills could have been erected only at an incredible cost of labor. The careful measurements which have been taken of several of the principal mounds have enabled explorers to make an accurate calculation of the exact amount of labor employed on each. The result is startling, even though one is prepared for something enormous. The great mound of Koyunjik--which represents the palaces of Nineveh itself--covers an area of one hundred acres, and reaches an elevation of 95 feet at its highest point. To heap up such a pile of brick and earth "would require the united exertions of 10,000 men for twelve years, or of 20,000 men for six years."[L] Then only could the construction of the palaces begin. The mound of Nebbi-Yunus, which has not yet been excavated, covers an area of forty acres and is loftier and steeper than its neighbor: "its erection would have given full employment to 10,000 men for the space of five years and a half." Clearly, none but conquering monarchs, who yearly took thousands of prisoners in battles and drove home into captivity a part of the population of every country they subdued, could have employed such hosts of workmen on their buildings--not once, but continually, for it seems to have been a point of honor with the Assyrian kings that each should build a new palace for himself. [Illustration: 12.--TERRACE WALL AT KHORSABAD. (Perrot and Chipiez.)]