Where Does the #Hashtag Symbol Come From?

S1, E4: It’s gone by many names, (the pound sign, the number sign, the octothorpe and the hashtag symbol) and it’s had many meanings, but what is the origin of this # mysterious symbol? Well the truth is it goes back all the way to ancient Rome. But what’s even stranger is that the hashtag symbol can help us understand the always changing nature of the abstraction that is language itself.