Civilization V: The Celtic Chronicle, part 1 (4000 B.C. to 1150 B.C.)

T.J. Hafer at

STONEHENGE!

1500 B.C.: Construction is completed on STONEHENGE! It is of the proper proportions, and in no danger of being trod upon by the wee folk.
Much like the historical Celts, I've beaten everyone to being the first civilization to stack a bunch of big rocks together in a circle. This grants me a huge bonus to Faith generation.

Later that year, the Celts capture French refugees trying to flee Paris and send them back to Celtica to replace the lost workers taken by the barbarians.

Additionally, the Swedes approach the Celts asking for aid in a war against the Germans. They decline, despite the Swedish leader's epic beard.
I have nothing against the Swedes at this point, but diverting any troops to a second war would be too costly to my efforts in France. Besides, I have no compelling reason to ruin my friendship with Germany.

1500 B.C. Pretty big year.