Have a fully educated population with 200 adults for 4 years.
This is another that should be achievable through normal gameplay. Your should always ensure that your citizens are educated in order to have them the most productive.
Tips
Make sure to build schools early on, so that you don't get too many uneducated labourers at the start.
Don't accept any nomads, as they will arrive uneducated, and you won't be able to get them educated.