In the late fourth century AD, the Roman taxman wanted gold above all else. Taxes were only payable in gold. It was by far the most valuable material available, so payments in gold made transferring large amounts of money over long distances easier for the state than bulky silver and bronze. Gold was also regarded as the most stable in value of all monetary materials.To ensure the continued purity of the gold coinage, in about AD 367 the emperors ordered all gold coins paid in tax to be melted down into bars before being turned back into coin. There were many forgeries about and it was easier for the government to test a smaller number of large bars than millions of individual coins. Roman gold coins were about 98% pure, as compared to modern British gold sovereigns which only contain 92% pure gold.These gold bars represent the intermediate form which the gold took after melting and before it was turned back into coins. They are marked with official assayers' stamps, which demonstrate the quality of the metal.