Seleucus, who had founded a kingdom in Media and Persia, feeling himself unable to vanquish Chandragupta, sent a Greek named Megasthenes to reside at his court at Pataliputra. This ambassador thus lived for several years in the heart of India between 311 and 302 B.C., and wrote a work entitled Ta Indika, which is particularly valuable as the earliest direct record of his visit by a foreigner who knew the country himself. Megasthenes furnishes particulars about the strength of Chandragupta's army and the administration of the state. He mentions forest ascetics (Hylobioi), and distinguishes Brachmanes and Sarmanai as two classes of philosophers, meaning, doubtless, Brahmans and Buddhists (çramanas). He tells us that the Indians worshipped the rain-bringing Zeus (Indra) as well as the Ganges, which must, therefore, have already been a sacred river. By his description of the god Dionysus, whom they worshipped in the mountains, Çiva must be intended, and by Herakles, adored in the plains, especially among the Çurasenas on the Yamuna and in the city of Methora, no other can be meant than Vishnu and his incarnation Krishna, the chief city of whose tribe of Yadavas was Mathura (Muttra). These statements seem to justify the conclusion that Çiva and Vishnu were already prominent as highest gods, the former in the mountains, the latter in the Ganges Valley. Krishna would also seem to have been regarded as an Avatar of Vishnu, though it is to be noted that Krishna is not yet mentioned in the old Buddhist Sutras. We also learn from Megasthenes that the doctrine of the four ages of the world (yugas) was fully developed in India by his time. Chandragupta's grandson, the famous Açoka, not only maintained his national Indian empire, but extended it in every direction. Having adopted Buddhism as the state religion, he did much to spread its doctrines, especially to Ceylon, which since then has remained the most faithful guardian of Buddhist tradition.