system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What year did people thousands of years ago think they were in? What year did they think it was in 100 BC? 1000 BC?

EDIT: As people have brought up, it depends on the people and place, so for clarity, if possible please include the part of the world/people you are talking about that thought this way.
gpt
> Did they count down the years at the time, like BC

They couldn't have. They'd have no idea what to count down to.

> did they count up, like AD

Usually they did, however when they count up from varied.

For example the Mayans (of 2012 fame) had a calendar based on counting the days since 'creation', which happens to be August 11, 3114 BC on our modern calendars. So for example August 31, 3114 BC to a Mayan would be day 20 and  December 21, 2012 is day 1,872,000.

Other cultures based their years on the reign of their current monarch. So a date may be recorded as March 15, in the 3rd year of King Derp; or something similar. It's this system which was used in our current calendar, using the birth of Christ instead of the rise of a monarch.