The Woad March
2175 B.C.: The Celtic chieftain puts his riches to use hiring fierce Picts from the forests around Edinburgh. The tattooed warriors begin what comes to be known as the Woad March toward Paris.
I spent nearly all of my gold to bypass the training time and get two units of my unique troops out at once. In addition to giving me Faith with every kill, they should provide me with enough sheer military weight to overwhelm Paris without those stupid Russians.
2100 B.C.: The English request an embassy in Edinburgh. The Celts refuse, assuring the English that it's absolutely not because they have plans to conquer them and take all of their gold. They just... don't feel like it right now.
I run the risk of making England suspicious by turning down their embassy, but it's better than becoming friends and then attacking them later. Doing so would make the AI perceive me as an untrustworthy ally. If you plan to burn someone off the map in Civ V, it's best to maintain cold relations until you're ready to do it.
Later that year, the Celtic writing system is formalized.
1925 B.C.: The Picts emerge out of the jungles north of a Paris already burning from Celtic raids. The long Siege of Paris begins.