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