Coins appeared in the Greek-speaking world approximately in the 7th century BCE in Asia Minor (today Turkish Aegean coast). Coins were originally made from silver or electrum, and later from gold and copper coins. Coin masters were highly respected, and there were important officials overseeing the minting system. Stater, the oldest type of coin, was of different weight depending on its place of origin. A Greek stater inspired by Persia was made with 12 parts of gold to 1 part silver, its value corresponded to 20 drachmae. Other types included the lepton (silver, 5 mm, a hundredth¨of drachma) the silver drachma (40 mm, 40 g of silver), and the didrachm and tetradrachm. For many years the information about the time of origin was missing on but coins from the Hellenistic era provided not only the names of the rulers but also the officials. The motifs most often included deities (such as Athena) and the rulers, and on the reverse there might have been animals, inscriptions, a symbol, or maybe another deity. Even Aristotle expressed an interest in the study of coins in his writings.