which stimulated the economy and increased trade across his empire. However, Alexander's constant demands for troops and the migration of Macedonians throughout his empire depleted Macedon's strength, greatly weakening it in the years after Alexander, and ultimately led to its subjugation by Rome after the Third Macedonian War (171–168 BC). Coinage The conquest by Philip II of Pangaeum and then of the island of Thasos between 356 and 342 BC brought rich gold and silver mines under Macedonian control. Alexander appears to have introduced a new coinage in Cilicia in Tarsus, after the Battle of Issus in 333 BC, which went on to become the main coinage of the empire. Alexander minted gold staters, silver tetradrachms and drachims, and various fractional bronze coins. The types of these coins remained constant in his empire. The gold series had the head of Athena on the obverse and a winged Nike (Victory) on the reverse. The silver coinage had a beardless head of Heracles wearing a lionskin headdress on the obverse and Zeus aetophoros ('eagle bearer') enthroned with a scepter in his left hand, on the reverse. There are both Greek and non-Greek aspects to this design. Heracles and Zeus were important deities for the Macedonians, with Heracles considered to be the ancestor of the Temenid dynasty and Zeus the patron of the main Macedonian sanctuary, Dium. However, the lion was also the symbolic animal of the Anatolian god Sandas, worshipped at Tarsus. The reverse design of Alexander's tetradrachms is closely modelled on the depiction of the god Baaltars (Baal of Tarsus), on the silver staters minted at Tarsus by the Persian satrap Mazaeus before Alexander's conquest. Alexander did not attempt to impose uniform imperial coinage throughout his new conquests. Persian coins continued to circulate in all the satrapies of the empire. Indian campaign Forays into the Indian subcontinent After the death of Spitamenes and his marriage to Roxana (Raoxshna in Old Iranian) to cement relations with his new satrapies, Alexander turned to the Indian subcontinent. He invited the chieftains of the former satrapy of Gandhara (a region presently straddling eastern Afghanistan and northern Pakistan), to come to him and submit to his authority. Omphis (Indian name Ambhi), the ruler of Taxila, whose kingdom extended from the Indus to the Hydaspes (Jhelum), complied, but the chieftains of some hill clans, including the Aspasioi and Assakenoi sections of the Kambojas (known in Indian texts