Credits of Mass and Energy. Abbreviated as MECs, these are used as currency on Gaea within the Tanager Grid System. MECs replaced the metric currency system used on Gaea during the height of the Roman Empire, which included the following units: Denarius — /de.ˈnaː.ri.us/ (deh-NAH-ree-oos) was the largest denomination in Roman culture on Gaea. Plural: denarii — /de.ˈnaː.ri.iː/ (deh-NAH-ree-ee). Assarius — /as.ˈsaː.ri.us/ (ah-SAH-ree-oos). Plural: assarii — /as.ˈsaː.ri.iː/ (ah-SAH-ree-ee). Ten assarii made one denarius. Semi — /ˈse.mi/ (SEH-mee). Two of these made one assarius. It was the smallest denomination in Roman culture on Gaea.