Here is the full list of all 20 Age of Empires: Castle Siege achievements worth 200 gamerscore.
Unlocked each civilization's unique troop
Destroyed 30 Emplacements in Multiplayer Battles
Unlocked any 6 heroes
Looted 60,000 Stone
Destroyed 40 Walls in Multiplayer Battles
Looted 100,000 Wood
Successfully defended your castle 10 times
Looted 30,000 Food
Advanced to the Second Age
Unlocked the Raiders from the Barracks
Unlocked the Catapult from the Siege Workshop
Upgraded an Archer Tower to level 5
Built a Stable
Win 3 battles in the Historical Campaign
Win 20 Multiplayer Battles
Win 100 Crowns in Multiplayer Battles
Destroy the Keep 100 times in Multiplayer Battles
Advance to the Eighth Age
Win 2000 Crowns in Multiplayer Battles
Upgrade all civilizations' unique troop to level 4