The solidus was introduced by Constantine the Great in c. AD 312 and was composed of relatively solid gold. Constantine's solidus was struck at a rate of 72 to a Roman pound (of about 326.6 g) of gold; each coin weighed 24 Greco-Roman carats (189 mg each), or about 4.5 grams of gold per coin. By this time, the solidus was worth 275,000 increasingly debased denarii, each denarius containing just 5% silver (or one twentieth) of the amount it had three and a half centuries beforehand. With the exception of the early issues of Constantine the Great and the odd usurpers, the solidus today is a much more affordable gold Roman coin to collect, compared to the older aureus, especially those of Valens, Honorius and later Byzantine issues.