We don't know what the Great Bath was used for, but since later Indian culture placed a huge emphasis on ritual purity, which is the basis for the caste system, some historians have speculated that the bath might have been like a giant baptismal pool. Also, they traded. One of the coolest things that the Indus Valley civilization produced were seals, used as identification markers on goods and clay tablets. These seals contain the writing that we still can't decipher and a number of fantastic designs, many featuring animals and monsters. One of the most famous and frightening is of a man with what looks like water buffalo horns on his head, sitting cross-legged between a tiger and a bull. We don't know what's really going on here, but it's safe to say that this was a powerful dude because he seems to be able to control the tiger. How did these seals let us know that they traded?