This is a rough guide provided by me, [DREAM] x Legend x on how to play the civilization Celts in deathmatch for HD. Hope you enjoy!
Build Order to start:
1 stable, 6 barracks, 10-12 siege workshops, castles as appropriate.
Siege Onager, Heavy Scorpion, Siege Ram, Woad Raider - You can also mix in Champion / Halb / Paladin / Hussar to protect your Celt Siege or to raid as appropriate. Trebuchets are ideal for dealing with enemy castles.
I like to play Celts defensively, often countering an enemy push with the defenders advantage. Be careful not to get out flanked or surrounded though if you are playing defensive as Celts are a relatively fast civilization.
Celts are a costly civilization with a wood heavy economy.
I hope you appreciated my guide on how to play Celts, let me know if you have anything to add or any questions!