73567
From the beginning of the 2nd century BC , power was contested between two groups of aristocrats : the optimates , representing the conservative part of the Senate , and the populares , which relied on the help of the plebs ( urban lower class ) to gain power .
 Senate
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Senate