[Illustration: Brit. Mus., No. 86261.--Brit. Mus., No. 86260.--THE BLAU MONUMENTS.] The second important point on which opinion is not agreed, concerns the relation of the First Dynasty of Babylon to that of Isin. From the Nippur dynastic list we know the duration of the dynasties of Ur and Isin, and if we could connect the latter with the First Dynasty of Babylon, we should be able to carry a fixed chronology at least as far back as the age of Gudea. Such a point of connection has been suggested in the date-formula for the seventeenth year of Sin-muballit's reign, which records a capture of Isin; and by identifying this event with the fall of the dynasty, it is assumed that the kings of Isin and of Babylon overlapped for a period of about ninety-nine years. In a later chapter the evidence is discussed on which this theory rests, and it is shown that the capture of Isin in Sin-muballit's seventeenth year had nothing to do with the dynasty of that name, but was an episode in the later struggle between Babylon and Larsa.[14] We thus have no means of deciding what interval, if any, separated the two dynasties from one another, and consequently all the earlier dates remain only approximate. The contract-tablets dating from the period of the Dynasty of Isin, which have been found at Nippur, are said to resemble closely those of the First Babylonian Dynasty in form, material, writing, and terminology.[15] It would thus appear that no long interval separated the two dynasties from one another. We have seen that the foundation of the Babylonian monarchy may be set in about the middle of the twenty-first century B.C., and by placing the end of the Dynasty of Isin within the first half of that same century we obtain the approximate dates of 2300 B.C. for the Dynasty of Isin, and 2400 B.C. for the Dynasty of Ur. It is true that we know that the Dynasty of Ur lasted for exactly one hundred and seventeen years, and that of Isin for two hundred and twenty-five years and a half, but until we can definitely connect the Dynasty of Isin with that of Babylon, any attempt to work out the dates in detail would be misleading. We must be content to await the recovery of new material, and meanwhile to think in periods.