Wow. The Celts are actually a pretty good civilization to play!
Building 2 scouts and 2 scout boats I was able to contact everyone except the jorubans, zulus and american civs, and also visit most of the goody huts for lots of techs!
Then I made a bit of a land grab gambit and didn't go for ireland, instead going for northern france, denmark, norway and sweden.
Then I decided to take out the vikings' naval capabilities and got Rostov and Grobina, their 2 cities on the baltic, and eventually Konugard near the black sea.
Meanwhile, to avoid what always happened in my other games, I made use of the Theocratic govt for one very important purpose: slow down other nations' development. This would be impossible with oligarchic republic beacuse the war weariness would be too great after 150 turns:
Basically in my previous games, Ethiopia was always a huge economic, scientific and military powerhouse. In order to make them focus more resources on military rather than science, as soon as they declared war (I refused to give them 100 gold even though I had 5000 hahah), I got as many ppl as I could against them - carthage and babylon in this case. Not Rome, for 2 reasons: ethiopia hired them to fight me, and most importantly: I don't wanna break a military alliance and I wnated to conquer Roma
So with my new knights (thanks to Grobina's horses) and a knight army, I conquered France, Austria, and started massing my forces for a huge assault on Roma. Meanwhile the vikings had captured or settled the eastern roman territory, and I slowly went down there too with leftover knights and gallic swordsmen.
That's when Mongolia declared war haha. Damn those keshiks! Good thing at that point (in the early 1400's) I discovered firearms, and was also able to build longbowmen in my viking cities thanks to workers buildilng roads.
Still it wasn't enough, so in a short cease of fire with the vikings I made military alliances with the vikings, indians and chinese against the mongols.
Then my knights army, 10 knights and 5 gallic swordsmen attack Roma and took it! But they weren't destroyed yet.. After conquering Vibo Valentia from Scandinavia, I discovered Rome had one crossbowman and one settlers stationed besides that city, and they weren't moving. Roman nomads haha! Eventually ethiopia made them declare war, and I destroyed them.
Carthage is nearly destroyed too, they have one city in Africa (near that volcano to the west) and 2 in spain. Babylon is in poor shape too as they were assailed by the ethiopians AND the indians. Surprisingly, the jorubans and zulus are still alive in the early 1500's, and ethiopia is barely more advanced than I (only one more tech, Magnetism), unlike previous games.
China has a few more techs though, I will have to catch up - but all the wars I waged made my science and economy pretty weak, thankfully I'm slowly building everything as my borders move forward.
Conclusions: celts are AWESOME. Building scouts and scout boats before anything else is a great strategy with this mod too!