With the coming into power of the Tang dynasty at the close of a long period of civil warfare there was perceptible progress in trade - mainly due to the attempt at standardizing currency during their rule. The coins of this period were extremely simple of manufacture, and being mostly in copper, their manufacture by unauthorised process grew to be a nuisance. In every part of the country the authorised coins were swamped with counterfeit issues and the chronicles of currency under this dynasty were no more than monotonous repetitions of harsh laws against counterfeiters. It is recorded in history that when counterfeiting on land became dangerous coiners transferred their operations to vessels and rafts in the rivers. The result was the issuance of an edict to the effect that when over a hundred catties of copper and tin were found on board a vessel the government had the right of confiscating it. In modern times in civilized States, the process by which coins are minted is so complicated and scientific that counterfeiting becomes extremely dangerous. The mechanical execution of modern coins is so perfect as to make forgery impossible - although, however, it is well known that counterfeiters have also taken advantage of the progress of modern science and produced coins not very easy of detection. In modern times the coins are struck and the edges are milled. In ancient China, on the other hand, the crude practice of casting the coins in moulds was adopted - a practice that was in vogue, even at the close of the 19th century. It was easy, therefore, to obtain a copy of the mould and for a clever counterfeiter to go on making exact copies of the government's coins.