Political and economic discussions of inequality have boomed since the second half of the twentieth century, but concepts of equality and inequality are far older. Understanding the longer intellectual history of inequality helps deepen understandings of how the concept has changed over time, as well as across different societies, and how concepts of equality have been pre-figured to accommodate concepts of inequality. Concepts of equality have been informed by culturally relative theories of justice and beliefs about institutions that can help rationalise situations of inequality. This article examines how Scholastic examinations of equality in Europe during the Middle Ages came to focus both on the importance of property and proportionality, the need to differentiate between people of different status, and how this was developed by the so-called Second Scholastics during the emergence of the Spanish Empire in the sixteenth century and helped lay the foundations for the concepts of inequality that came to structure global imperialism.