To overcome this difficulty and keep their peace with the Gods of their Fathers, the Sumerians had built a number of low towers (resembling little hills) on the top of which they had lighted their sacred fires in honor of the old divinities. When the Jews visited the town of Bab-Illi (which we call Babylon) many centuries after the last of the Sumerians had died, they had been much impressed by the strange-looking towers which stood high amidst the green fields of Mesopotamia. The Tower of Babel of which we hear so much in the Old Testament was nothing but the ruin of an artificial peak, built hundreds of years before by a band of devout Sumerians. It was a curious contraption. The Sumerians had not known how to construct stairs. They had surrounded their tower with a sloping gallery which slowly carried people from the bottom to the top. A few years ago it was found necessary to build a new railroad station in the heart of New York City in such a way that thousands of travelers could be brought from the lower to the higher levels at the same moment. It was not thought safe to use a staircase for in case of a rush or a panic people might have tumbled and that would have meant a terrible catastrophe. To solve their problem the engineers borrowed an idea from the Sumerians. And the Grand Central Station is provided with the same ascending galleries which had first been introduced into the plains of Mesopotamia, three thousand years ago. ASSYRIA AND BABYLONIA--THE GREAT SEMITIC MELTING-POT We often call America the "Melting-pot." When we use this term we mean that many races from all over the earth have gathered along the banks of the Atlantic and the Pacific Oceans to find a new home and begin a new career amidst more favorable surroundings than were to be found in the country of their birth. It is true, Mesopotamia was much smaller than our own country. But the fertile valley was the most extraordinary "melting-pot" the world has ever seen and it continued to absorb new tribes for almost two thousand years. The story of each new people, clamoring for homesteads along the banks of the Tigris and the Euphrates is interesting in itself but we can give you only a very short record of their adventures. [Illustration: HAMMURAPI.] The Sumerians whom we met in the previous chapter, scratching their history upon rocks and bits of clay (and who did not belong to the Semitic race) had been the first nomads to wander into Mesopotamia. Nomads are people who have no settled homes and no grain fields and no vegetable gardens but who live in tents and keep sheep and goats and cows and who move from pasture to pasture, taking their flocks and their tents wherever the grass is green and the water abundant. Far and wide their mud huts had covered the plains. They were good fighters and for a long time they were able to hold their own against all invaders.