Are we in a position to fix even approximately the period at which the settlement of the Aryas in the valley of the Ganges took place, and the struggles connected with this movement came to an end? The law-book of the Indians tells us that the world has gone through four ages; the age of perfection, _Kritayuga_; the age of the three fires of sacrifice, _i.e._ of the complete observance of all sacred duties, _Tritayuga_; the age of doubt, _Dvaparayuga_, in which the knowledge of divine things became obscured; and lastly the age of sin, the present age of the world, _Kaliyuga_. Between the end of one period and the beginning of the next there came in each case a period of dimness and twilight. If this period is reckoned in, the first age lasted 4800 divine years, or 1,728,000 human years; the life of men in this age reached 400 years. The second age lasted 3600 divine years, or 1,296,000 human years, and life reached 300 years. The third age lasted 2400 divine years, or 864,000 human years, and men only lived to the age of 200 years. The present age will last 1200 divine years, or 432,000 human years, and men will never live beyond the age of 100 years.[124] This scheme is obviously an invention intended to represent the decline of the better world and the increase of evil, in proportion to the distance from the divine origin. In the matter of numbers the Indians are always inclined to reckon with large figures, and nothing is gained by setting forth the calculations in greater detail. From the Rigveda it is clear that the year of the Indians contained 360 days in twelve months of 30 days. In order to bring this year into accordance with the natural time, a month of thirty days was inserted in each fifth year as a thirteenth month although the actual excess in five years only amounted to 26-1/4 days. Twelve of these cycles of five years were then united into a period of 60 years, _i.e._ 12 x 5, and both the smaller and the larger periods were called _Yuga_.[125] On this analogy the world-periods were formed. By multiplying the age of sin by ten we get the whole duration of the world; the perfect age is four times as long as the age of sin.[126] A year with the gods is as long as a day with men; hence a divine year contains 360 years of men, and the world-period, _i.e._ the great world-year, is completed in 12 cycles each of 1000 divine years, _i.e._ 360,000 human years. In the first age, the age of perfection, Yama and Manu walked and lived on earth with their half-divine companions (p. 30); in the age of the three fires of sacrifice, _i.e._ of the strict fulfilment of sacred duties, lived Pururavas, who kindled the triple sacrificial fire,[127] and the great sacrificers or minstrels, the seven or ten Rishis (p. 29 _n._ 2); the period of darkness and doubt was the age of the great heroes. With the priests who invented this system of ages the period of the great heroes was naturally placed lower than that of the great sacrificers and saints.