Sources for A Celtic Campaign?

[Palanan]

I'm looking for good sources of information for a possible Celtic campaign, both in terms of gaming supplements as well as solid historical material.

I'm aware of the 2E Moonshae supplement for the Forgotten Realms, and wouldn't mind seeing similar sourcebooks, maybe for Pathfinder/Golarion or other settings. But I'm just as interested in the history and archaeology of the Celtic peoples, and naturally their legends as well. Can anyone suggest some good reading that would cover these topics?

[sabelo2000]

Stephen R. Lawhead writes good Celtic fiction, check out his Song of Albion series or his Celtic take on the Arthur legends. The Mabinogion is a collection of old Celtic legends, you can find it at most bookstores. Other than that I don't know any specifics, check out your library or online for an anthology of Celtic mythology or some history books.

[Black Jester]

Well, there is a Gurps book for that. (http://www.sjgames.com/gurps/books/Celtic/) Even though the mechanical aspects are probably useless to you, it is still a gurps book, so the chances are high that it is the best RPG resource you will find for that topic.
There was also a 'historical reference' sourcebook about Celts (http://rpg.drivethrustuff.com/product/110199/HR3-Celts-Campaign-Sourcebook-(2e)) for AD&D, but the historical references sourcebooks tended to be somewhere between okay and slightly underwhelming, and the mechanics are probably also useless to you.

[Grinner]

Were you looking for free resources, or are you willing to spend money? Because there's a boatload of celt-themed d20 RPGs.

[Gemini Lupus]

There's a wealth of resources for a Celtic Campaign, depending on what you're looking for. For a 3.x take on the Celts, Black Jester listed two of the resources I was going to suggest, but there's also a take on an Arthurian campaign (http://www.amazon.com/Relics-Rituals-Excalibur-Sword-Sorcery/dp/1588469565) or this take on the Celtic peoples in general. (http://www.ebay.com/ctg/Celtic-Age-Roleplaying-Myths-Heroes-and-Monsters-Celts-Avalanche-Press-2002-Paperback-/2663085) I personally own both of these and am satisfied with the info.

You can also do independent research on the Celts, there's many good historians who have published books about them. I can recommend anything written by Peter Beresford Ellis, Terry Jones' Barbarians has a good segment dedicated to the Celts, Jean Markale and Barry Cunliffe are both respected historians on the topic. I myself am a grad student in history, specializing in the Middle Ages, with an emphasis/passion on/for the Celtic peoples, so if you have any questions, I'll be happy to answer them either here or through PM.

Also, Wikipedia will give you a decent overview.