Entirely new conditions arose when the population grew until agriculture became a necessity for the production of sufficient food. The influence of the Sun now became so dominating that it must be given the first place among the powers that affect the fates of men. The plants have a decided annual period and so have the overflows of the rivers which were of the utmost importance in those countries where the cradle of civilization stood. The rainfalls themselves were of annual recurrence as were also the intervening droughts. In Egypt the great importance of the floods caused the introduction of the solar year at a very early stage and its length was fixed at 12 months of 30 days, or 360 days, so that the beginning of the year occasionally had to be adjusted. This was accomplished by resorting to observations of the rising and setting of the Dog Star or Sirius. Thus we realize how difficult it was to determine the exact length of the solar year from everyday phenomena. The great reformer Amenhotep IV. endeavoured about 1400 B.C. to have the Sun-god recognized as sole master of all the world. He met, however, with such great obstacles on the part of the conservative priesthood, which as they largely were serving different gods would have lost part of their power if the reform had prevailed, that his successor was obliged to yield to the solid opposition. In Babylon the local god Marduk, once representative of the planet Jupiter, and among the star-gods ranking next to the three Super-gods, became about 2000 B.C. elevated to the highest position among the gods and assumed at the same time the dignity of Sun-god. It may here be mentioned that Marduk also played a great part as healer of illness. The evolution in ancient Rome followed the same course although at a far later time. Emperor Aurelianus (270–275 A.D.) under the influence of oriental Mithras-cult elevated the Sun-god to supreme god of the whole Roman Empire, which then comprised almost the entire known world.