Celts/Tree

The Celts have access to the following buildings, units and technologies:

Archery Range
Units
 * Archer -> Crossbowman
 * Skirmisher -> Elite Skirmisher
 * Cavalry Archer -> Heavy Cavalry Archer

Barracks
Units Technologies One of the Celts' civilization bonuses is +15% infantry speed. This bonus means Celtic infantry are quicker than those with Squires by 5% speed (without the upgrade).
 * Militia -> Man-at-Arms -> Long Swordsman -> Two-Handed Swordsman -> Champion
 * Spearman -> Pikeman -> Halberdier
 * Tracking

Stable
Units Technologies
 * Knight -> Cavalier -> Paladin
 * Scout Cavalry -> Light Cavalry -> Hussar
 * Husbandry

Dock
Units Technologies
 * Fishing Ship
 * Trade Cog
 * Fire Ship
 * Transport Ship
 * Demolition Ship -> Heavy Demolition Ship
 * Galley -> War Galley -> Galleon
 * Cannon Galleon
 * Gillnets
 * Careening -> Dry Dock
 * Shipwright

Watch Tower
Can be upgraded to:
 * Guard Tower -> Keep

Stone Wall
Can be upgraded to:
 * Fortified Wall

Monastery
Units Technologies
 * Monk
 * Fervor
 * Sanctity
 * Herbal Medicine
 * Heresy
 * Illumination
 * Faith

Castle
Units Technologies
 * Woad Raider -> Elite Woad Raider
 * Petard
 * Trebuchet
 * Stronghold
 * Furor Celtica
 * Hoardings
 * Sappers
 * Conscription
 * Spies/Treason

Town Center
Units Technologies
 * Villager
 * Town Watch -> Town Patrol
 * Feudal Age -> Castle Age -> Imperial Age
 * Loom
 * Wheelbarrow
 * Hand Cart

Siege Workshop
Units
 * Mangonel -> Onager -> Siege Onager
 * Battering Ram -> Capped Ram -> Siege Ram
 * Scorpion -> Heavy Scorpion

Blacksmith
Technologies
 * Padded Archer Armor -> Leather Archer Armor
 * Fletching -> Bodkin Arrow
 * Forging -> Iron Casting -> Blast Furnace
 * Scale Barding Armor -> Chain Barding Armor
 * Scale Mail Armor -> Chain Mail Armor -> Plate Mail Armor

University
Technologies
 * Masonry
 * Fortified Wall
 * Chemistry
 * Ballistics
 * Siege Engineers
 * Guard Tower -> Keep
 * Heated Shot
 * Murder Holes
 * Treadmill Crane

Mining Camp
Technologies
 * Stone Mining -> Stone Shaft Mining
 * Gold Mining -> Gold Shaft Mining

Lumber Camp
Technologies
 * Double-Bit Axe -> Bow Saw

Market
Units Technologies
 * Trade Cart
 * Cartography -> Caravan
 * Guilds
 * Coinage -> Banking

Mill
Technologies
 * Horse Collar -> Heavy Plow