the conflict of which yaman had been the theatre ever since the fourth century c.e. influenced the distribution of population in the arabian peninsula. it is told that the dam of ma'rib, by means of which the himyaris changed the course of nature to benefit their country, was destroyed by the great flood, "sayl al arim," with the result that large sections of the inhabitants had to migrate. apparently the continuing political conflicts so distracted men and governments from attending to the repair and maintenance of the dam that when the flood came it was incapable of holding the water. it is also told that the shift in population was due to the fact that the byzantine emperor, realizing the threat to his trade by the conflict with persia over yaman, built a fleet of ships to ply the red sea and thereby avoid the caravan routes of arabia. historians agree on the historicity of the immigration of the azd tribes from yaman to the north but disagree in explaining it. some attribute it to the loss of trade, and others to the destruction of the dam of ma'rib and the resultant loss in food production. whatever the explanation, the historicity of the event is beyond doubt. it was at the root of the blood relation of the yamanis with the northern arabs and their involvement in the history of the north. even today the problem is still far from solved.