The largest pyramid, Cheops, rises to a height of 480 feet, having a base covering 13 acres. The historian Herodotus relates that 120,000 men were employed for 20 years in the erection of this great structure. It has never been explained how these people, not yet well developed in practical mechanics, and not having discovered the use of steam and with no {160} use of iron, could have reared these vast structures. Besides the pyramids, great palaces and temples of the kings of Thebes in Upper Egypt rivalled in grandeur the lonely pyramids of Memphis. Age after age, century after century, witnessed the building of these temples, palaces, and tombs. It is said that the palace of Karnak, the most wonderful structure of ancient or modern times, was more than five hundred years in the process of building, and it is unknown how many hundreds of thousands of men spent their lives for this purpose. So, too, the mighty sphinxes and colossal statues excite the wonder and admiration of the world. Especially to be mentioned in this connection are the colossi of Thebes, which are forty-seven feet high, each hewn from a single block of granite. Upon the solitary plain these mute figures sat, serene and vigilant, keeping their untiring watch through the passage of the centuries. _The Coming of the Semites_.--While the ancient civilization at the mouth of the Euphrates had its origin in primitive peoples from the mountains eastward beyond the Euphrates, and the ancient Egyptian civilization received its impetus from a Caucasian tribe of northern Africa, the great civilization from the Mediterranean Sea to the Indus River was developed by the Semites. Westward from the Euphrates, over Arabia, and through Syria to the Mediterranean coast were wandering tribes of Arabs. Perhaps the most typical ancient type of the Semitic race is found in Arabia. In these desert lands swarms of people have passed from time to time over the known world. Their early life was pastoral and nomadic; hence they necessarily occupied a large territory and were continually on the move. The country appears to have been, from the earliest historic records, gradually growing drier--having less regular rainfall.