This isn't my area, but my understanding is that like most things related to history (especially Indian history), it's complicated. There are a lot of very old

This isn't my area, but my understanding is that like most things related to history (especially Indian history), it's complicated. There are a lot of very old antecedents, but the modern caste system probably "originated" with the later Mughals. The British Raj took those scattered, vaguely related systems and codified them into what we recognize today.