Maurya emperor Chandragupta Maurya came up with the punch-marked coins, which were minted in silver, gold, copper, or lead. Indo-Greek Kushan kings introduced the Greek custom of engraving portraits on the coins. Chanakya, prime minister to the first Mauryan emperor, mentioned the minting of coins such as Rupyarupa (silver), Suvarnarupa (gold), Tamararupa (copper), and Sisarupa (lead) in his Arthashastra treatise. The major changes that took place in the economic sphere during Mauryan rule were increasing the use of coins, improving trade and commerce, improving communication and transportation, and so on. Mauryan coins were similar to the punch-mark silver coins of the Early Kingdoms. But Mauryan coins generally had five punches and also had a sun symbol in those punches. The coins issued by the Mauryans are mostly silver and a few copper pieces of metal in various shapes, sizes, and weights. They also have one or more symbols punched on them. The symbols included the elephant, the tree in the railing symbol, and the mountain. Some were geometrical symbols.