The expansion of two kingdoms in the northeast laid the groundwork for the emergence of India's first empire, ruled by the Mauryan dynasty (ca. 321–185 B.C.). According to the writings of the Greek diplomat Megasthenes, Pataliputra, the capital—surrounded by a wooden wall pierced by 64 gates and 570 towers—rivaled the splendors of contemporaneous Persian sites such as Susa and Ecbatana. By 303 B.C., Chandragupta Maurya (known to the Greeks as Sandracotta) had gained control of an immense area ranging from Bengal in the east to Afghanistan in the west and as far south as the Narmada River. Much of his success is attributed to his prime minister and mentor, Kautilya (also known as Chanakya), author of the Arthashastra, a cold-blooded treatise on the acquisition and maintenance of power. His son, Bindusara, extended the empire into central and parts of southern India. The third Mauryan emperor, Ashoka (r. ca. 273–232 B.C.), is one of the most famous rulers in Indian history. His conversion to and support of Buddhism is often likened to the impact of the Roman emperor Constantine the Great's acceptance of Christianity in 313 A.D. Beginning in 254 B.C., Ashoka had monumental edicts on Buddhism carved into rocks and caves throughout his empire. One records his sending of religious envoys—with no apparent results—to the Greek rulers of Syria, Egypt, Macedonia, Cyrene, and Epirus. Thirteen years later, he issued seven additional edicts carved into strategically placed polished sandstone pillars. One of the best preserved, at Lauriya Nandagarh in Bihar, stands thirty-two feet high and is capped by a seated lion. Ashoka is also credited with building 84,000 stupas to enshrine the relics of the Buddha and commemorate key events in the life of Siddhartha Gautama, the founder of Buddhism.