The next letter D, came from a representation of a door—“daleth” (dahleth). It probably pictures the door of a tent. A custom that prevails among the Arabs and in a number of countries gave particular importance to the door of a tent—a stranger, or even an enemy, if he entered through the door of a tent must receive food, drink and shelter. “Daleth” became “delta” with the Greeks and D (day) with the Romans, who, of course, rounded the angle.