
(from the article `ancient Rome`) ...allotted 30 centuries. In addition, there were 18 centuries of knightsmen wealthy enough to afford a horse for cavalry serviceand five other ...
Found on
http://www.britannica.com/eb/a-z/p/120

Proletarii was the name given to those Roman citizens who, in the classification of their means by Servius Tullius, stood in the sixth or lowest class.
Found on
http://www.probertencyclopaedia.com/browse/CXP.HTM
No exact match found.