What does Caius mean?
Common Roman form of Gaius. This was the name of the infamous Roman emperor called Caligula, a nickname meaning "little boots". This referred to the minature soldier's footwear he wore when he was young. A 16th-century English physician endowed a college at Cambridge University called "Gonville and Caius".
How popular is Caius?
Caius is an uncommonly occurring first name for men. Caius is an equivalently unusual last name too for all people. (2000 U.S. Census)
Below is a graphed comparison of the usage of the boy name Caius and corresponding names. The only popular variation form of Caius (outside Top 1000) ranked in the Top 1000 is Kay. Adoption of this boy name reached its peak during 1930-1939 (usage of 0.428%) and is now significantly less, with Kay becoming less fashionable. (2014 Birth Statistics)
Caius is pronounced similarly to Cass. Like Caius, this name is not frequently used.