If you want to be super technical, the real term is octothorpe. In terms of etymology, the ”octo-“ refers to “eight,” which is in reference to the points on the symbol. However, where “-thorpe” stems from is still up for debate. Some believe it was named after Olympian Jim Thorpe. Others do not agree and argue that it was just a random suffix.
By 285 CE the Roman Empire had grown so vast that it was no longer feasible to govern all the provinces from the central seat of Rome. The Emperor Diocletian divided the empire into halves with the Eastern Empire governed out of Byzantium (later Constantinople) and the Western Empire governed from Rome.