By the 5th Century B.C. three great cultures were in contact in the Eastern Mediterranean area. The newest of these, the Greek, began by borrowing and improving on the discoveries of Babylonians and Egyptians. The knowledge of the gnomon is attested as one such borrowing. An overview is attempted of the state of timekeeping, with particular emphasis on the measure of shadows, in these two older cultures, revealing the uncertainties as to just what they had to offer the Greeks, and how they had come to their conclusions.