Julius Caesar proposed the calendar in what we call the year 46 BC, but the Romans would have called it 'the year of the consulship of C. Julius Caesar and M. Aemilius Lepidus.' The Romans in that period did not use an absolute dating system. Like most other civilizations, they named the years after whoever was in charge. The Anno Domini system we use today wasn't invented until six centuries later, and not popularized for a couple of hundred years after that.