Along the coast plains and across the great Plain of Esdraelon ran the main highways that connected the three earliest and most nourishing centres of the world's civilization: the Egyptian on the southwest, the Amorite on the north, probably between the southern Lebanons, and the Babylonian to the east and northeast. For centuries the Canaanites had absorbed the ideas, institutions, and culture of these stronger peoples. So fundamentally had the Babylonians impressed the Canaanites that practically all of the inscriptions coming from this early period are written in the Babylonian script. Even in writing to their Egyptian conqueror during the fourteenth century, the Canaanite kings of Palestine used this same Babylonian system of writing. The Amorite civilization had so strongly influenced the Canaanites that to-day it is difficult for the archaeologist to distinguish between the two. By certain of the Biblical writers the terms Canaanite and Amorite are used interchangeably. As early as 1600 B.C. Egypt, under the ambitious conquering kings of the Eighteenth Dynasty, had overrun Palestine and for the next three or four centuries ruled it as a tributary province. The nearness of Egypt made its influence still more powerful, so that in nearly every mound and Canaanite ruin the excavator finds hundreds of reminders of the presence of the Egyptian civilization. The Canaanites had long since left behind them the nomadic state and had developed a strong agricultural and commercial civilization. Their life centered about certain important cities like Megiddo on the southwestern side and Bethshean on the eastern side of the Plain of Esdraelon. Their cities were usually built on a low-lying hill in the midst of rich encircling plains. They were provided with thick mud walls, behind which the inhabitants felt secure from attack. Over each city ruled a petty king, whose authority, however, did not extend far beyond the surrounding fields that belonged to the inhabitants of the town. Generally these city states were independent. In many cases they were hostile to each other; and the long rule of Egypt had tended to intensify this hostility, for Egypt had depended upon this local jealousy to maintain its control. The diversified physical contour of Palestine likewise strengthened this tendency toward separation rather than unity.