They constructed castles all over the country in order to control their newly-won territory, and to pacify the Anglo-Saxon population. These early castles were mainly of motte and bailey type.

Historically, the Anglo-Saxons did not build "castles" in the traditional sense that we imagine today; those were introduced to England by the Normans after the 1066 invasion. Instead, the Anglo-Saxons utilized burhs (fortified townships) and communal earthworks. The primary reason for building these was defense against Viking raids and to provide a secure network for trade and local governance. Unlike Norman castles, which were private fortified residences for a lord to control a hostile local population, Anglo-Saxon burhs were public works designed to protect the entire community. They were often large, walled settlements where people could take refuge. While there were a few pre-1066 "castles" built by Norman favorites of King Edward the Confessor (such as in Hereford), the vast majority of Anglo-Saxon military architecture focused on communal defense and administrative centers rather than the individual, private fortresses that defined the later feudal era.