But as long as you didn't yet have the GA, you should always be able do build new ones! Even in the 4th age...but at one point I was doing well enough that I just upgraded them & forgot about it.
Also keep an eye on any wonder that triggers the GA and beeline for it, before the AI gets it. For example the Internet triggers a GA for everyone, who still didn't have one!
Or specifically for the Celts, who need one agricultural and one religious wonder, any combination of Cure for Cancer/Universal Sufferage/Hoover Dam + a religious one would do it. So for example you could try and capture an AI city with a religious wonder (Zeus, Oracle, Knights Templar, Pyramids, Artemis, J.S.Bach's Cathedral or Sistine Chapel) and then beeline for Universal Sufferage or Hoover in the 3rd age, or for Cure for Cancer in the 4th age.


