The first two-wheeled carts were a great improvement upon the single rolling log, yet they were exceedingly heavy and clumsy. The trouble was with the wheel. This was very thick and with the exception of the hole in which the axle went it was entirely solid. Wheelwrights at a very early date saw that the problem was to make the wheel light and at the same time to keep it strong. Little by little this problem was solved. At first crescent-shaped holes were made in the wheel (Fig. 10). This made the wheel lighter, but did not weaken it. In its next form the wheel was even less solid than before. It now consisted of four curved pieces of wood (Fig. 11) held together by four spokes. In this wheel there was a hub, but the spokes were not inserted in it; they were fastened about it. In the Egyptian chariot (Fig. 12) we find the wheel in the last stage of its interesting and remarkable development. Here the spokes, six in number, are inserted in the hub from which they radiate to the six pieces of the felly or inner rim. Around the felly is the outer rim or tire made of wood and fastened to the felly with thongs. The wheel of to-day has more iron in it, and has more spokes and is lighter and stronger than the old Egyptian wheel, yet in its main features it is made like it. [Illustration: FIG. 11.--WHEELS WITH SPOKES. (From National Museum.)] [Illustration: FIG. 12.--AN ANCIENT EGYPTIAN CHARIOT SHOWING HUB, SPOKES, FELLY AND RIB. (From National Museum.)] [Illustration: FIG. 13.--WONDERFUL ONE HOSS SHAY. (From National Museum.)] A light running two-wheeled carriage was used by all the civilized nations of the ancient world. Three thousand years ago in the great and wicked city of Nineveh chariots raced up and down the paved streets "jostling against one another in the broad ways, with the crack of the whip, the rattle of the wheel and the prancing of horses." The chariot played an important part in the life of the Greeks and Romans, in their racing contests and in their wars, and throughout the Middle Ages it was the only vehicle in general use in Europe. As time passed it was of course made lighter and stronger and better. The doctor's gig so charmingly described by Holmes in his "Wonderful One Hoss Shay" may be taken as an illustration of the full development of the two-wheeled carriage (Fig. 13). [Illustration: FIG. 14.--AN ANCIENT ROMAN CHARIOT.]