''The Normans'' campaign consists of 10 missions, you can play at any difficulty to unlock the achievement. The hardest missions for this campaign are ''First Battle Of Lincoln'' and ''The Siege Of Wallingford'' because your tech level is low, your gold is limited (the marketplace is crucial to obtain gold at a certain point) and the enemy harassement is endless. I included videos for every mission of this campaign on hard difficulty to give you an idea how to beat them quickly and effectively. IMO, the best units to produce ASAP are the ''Mangonel'' and the ''Long Bow Archers''. Using these units mixed with some good micros will make things a lot easier when you face large armies and siege the enemy base.
The Normans Campaign (Longplay):1066: The Battle Of Hastings:1069: North To York:1105: The Fall Of Bayeux:1106: The Battle Of Tinchebray:1119: The Battle Of Brémule:1141: First Battle Of Lincoln: 1153: The Siege Of Wallingford1216: The Siege Of Dover1215: The Siege Of Rochester1217: Second Battle Of Lincoln