How were motte-and-bailey forts constructed in medieval Europe?

Motte-and-bailey castles were the earliest distinctive fortification of the feudal era, emerging in 10th- and 11th-century Europe. Their construction focused on two primary components:1

• The Motte: An elevated earth mound topped with a timber palisade and a keep, serving as the primary stronghold.12
• The Bailey: An outer compound at the base of the mound that housed barracks and other essential buildings, also protected by a palisade.31

Engineers separated these two areas with a defensive ditch, which was crossed by an elevated bridge to provide access to the motte. Early builders prioritized sites with available timber and suitable terrain. As feudal structures evolved, these timber designs were often replaced by stone, with the palisades giving way to masonry walls and the keep becoming a more permanent donjon. This design allowed for a tiered defense, where the garrison could retreat to the fortified keep if the outer bailey was breached.12