The Three Orders
Oratores, bellatores, laborares: this translates as "those who pray", "those who fight", and "those who work".
We find this three-fold division in writings as early as the 9th century, and it is commonly used right down to textbooks today. It was never a complete description of society, but it's a useful starting point because it will introduce some fundamental concepts and two important groups that appear over and over—the clergy and the nobility.
I will talk a bit about each of these groups in the following pages.