Journal or Book Title
Conflict in Ancient Greece and Rome: The Definitive Political, Social, and Military Encyclopedia
The Roman monetary system initially relie don bronze bullion (aes rude) but in the late fourth century BCE Rome began to cast heavy bronze coins (aes grave) and bars (aes signatum). By around 300 BCE the Romans had adopted Greek-syle silver coinage and they soon came to use lighter and more convenient fiduciary bronze coins.
Hollander, David B., "Coins" (2016). History Publications. 110.