The profession of the priesthood had certainly its mercenary aspect; sacrificial fees were fixed as well as sacrificial rites, and a not unimportant part of a ceremony was the offering of generous gifts to the Brahmans, who presided at the altar. But on the whole the riches thus expended were not given in vain. As in Egypt, the rise and endowment of the priestly cult was due to the accumulation of wealth which enabled a section of society to find leisure for study and the promotion of culture. Aryan civilization in India owed much to the Brahmans. They introduced and elaborated alphabetic signs; the devoted scholars among them compiled the first Sanskrit grammar and studied the art of composition. Among the hermits there were great and original thinkers who laid the basis of Indian metaphysical thought, and rose from the materialism of the early Vedic hymns to the idealism of the speculative prose works, which included the _Forest Books_, a name redolent of leafy solitude and of simple and contemplative lives on the banks of sweetly-flowing waters. Even their devotion to the mysteries of sacrificial ritual, which became more and more complicated, was not unproductive of permanent benefits to mankind. The necessity for the exact construction of altars, and the observance of ceremonies in due season, promoted the study of mathematical science. These Brahmans invented the numerical figures which have attained universal usage, and in time they gave the world Algebra. The influence of their culture may be traced in other directions. At the present day it has indirectly brought into existence the science of Comparative Religion. [Illustration: SADHUS (RELIGIOUS MENDICANTS) AT BENARES 16] At the close of the Rigvedic period the Aryans had extended their sway to the district known as Madhyadesa, the “middle country”, between the “Five Rivers” of the Punjab and the upper reaches of the Jumna and Ganges. Pioneers were meantime pressing southward and eastward towards the sea. Migrations were, no doubt, due to propulsion as well as attraction; fresh folk-waves probably poured in periodically from the north-west, while the settled population must have increased rapidly in the fertile land controlled by the invaders, to whom the aborigines offered but slight resistance.