Step 1: Understanding the Concept:
The question asks for the historical period in which the Varna system, the four-fold classification of Hindu society, originated.
Step 2: Detailed Explanation:
The earliest textual reference to the Varna system is found in the Purusha Sukta hymn, which is in the 10th Mandala (book) of the Rigveda.
The Rigveda is the foundational text of the Vedic period (c. 1500 - 500 BCE). Specifically, it was composed during the Early Vedic Period. Therefore, the concept of the Varna system originated during this era. There is no evidence of the Varna system in the earlier Harappan period.
Step 3: Final Answer:
The Varna system started in the Vedic period.