What is the meaning of Congius?

A Roman unit of liquid measure reckoned as the volume of 10 Roman pounds of wine and equivalent to about 3.3 L although differing slightly over time.

A Roman unit of mass instituted by Vespasian equivalent to about 3.3 kg, the weight of a congius of water.

congius, a Roman unit of liquid measure equivalent to about 3.3 L

congius, a Roman unit of mass equivalent to about 3.3 kg, the weight of a congius of water

Source: wiktionary.org