Breton Cavalry, Norman Army

We know that the English forces were stationed in a dense shield wall formation at the top of a slope (what more recent sources say was Caldbec Hill), with their flanks protected by woods and swampy ground ahead.
What is known of the Norman deployment is that Duke William appears to have organized his troops into 3 groups or 'battles'. The left 'battle' consisted mostly of Bretons and was led by Alan The Red.
The center was held by the Normans under the direct command of the duke, and the right was commanded by William Fitzosbern and Eustace II of Boulogne and consisted of French. and mercenaries from Picardy, Boulogne and Flanders.
The front lines of the invading forces consisted of archers, with a secondary line of foot soldiers armed with spears and swords. The cavalry was kept in reserve.
The Norman troop distribution implies that the plan was to open the fight with archers, weakening the enemy with arrows, followed by infantry who would engage the shield wall in close combat. The infantry would create openings in the English lines which would then be exploited by cavalry charges.
It is believed that due to the English's higher position on the crest, the early arrow fire probably had very little effect on the English shield wall.