The golden-wheel represents the gold-producing region, the silver-wheel stands for the region of the silver mines of the ancient world, and similarly copper and iron wheels identify the regions of copper and iron.
The Periplus, and also Pliny’s NH, mention the gold producing regions of the ancient world; according to the Periplus, gold was an export from Ommana only; it was a product of Ganges region; It was this production that led the Assyrian Tiglath-Pilaser III to refer to gold as the ‘dust of the country’ of Merodach-Baladan, King of Bit-Yakin. ‘Land of Havilah’( of Genesis II,11-12), which could rapidly supply caravans for Chaldaea, and ‘Land of Ophir’ of Solomon(I Kings X) were famous for gold. Agatharchides and Pliny(II,50) were both acquainted with the apyron gold, and Pliny(VI,23) mentions also a river Apirus in Carmania, in a region previously described by Alexander’s admiral, Onesicritus, as gold producing.
While Periplus says copper as wan exported from India to Persian Gulf, Pliny speaks (VI, 26) of copper, iron, arsenic, and red lead as exports of Carmania, and the Bible mentions Punon as a copper producing region, and Og as having an iron and copper mines within its region; Philistine monopoly on iron is seen from the Bible also. From Homeric epics it is learnt that the region on the banks of the river Scamander was a silver producing area. The Bible also speaks of Bronze Sea and Bronze Mountains.
Pliny says iron ore ‘is found almost everywhere, even in the Isle of Elba’. The best iron, according to him was made by the Sere and next to this was the Parthian iron.
Asoka at the time of his enthronement was not a Chakravartin, i.e the ruler of the ‘four quarters of the world’; on assuming first the iron-wheel status of a monarch, once he was going though the Jambudvipa on a tour of inspection at which time, he saw one of the places of torment for punishment of wicked men situated between the two iron-circle mountains.