What was the Roman hierarchy?

The Roman hierarchy in the beginning was separated into 2 levels. The Patricians: They were BORN into this family. So they are nobles. Then the Plebians: These people where mainly artistans or peasants. Then when the Roman Empire had started 2 more levels where added. The Middle Class: People who had started as Plebians but had now made buisnesses and where making money but not as much as the Patricians. And The Army: They obviously went to the army.