Chester city walls is made up of a defensive structure built to protect the city of Chester in Cheshire, England. Their erection was started by the Romans when they established the fortress of Deva Victrix between 70 and 80 AD. It was originally constructed with a rampart of earth and turf surmounted by a wooden palisade. From about 100 AD they were reconstructed using sandstone, but were not completed until over 100 years later. Following the Roman occupation nothing is known about the condition of the walls until Æthelflæd refounded Chester as a burgh in 907. The defences were improved, although the precise nature of the improvement is not known. After the Norman conquest, the walls were extended to the west and the south to form a complete circuit of the medieval city. The circuit was probably complete by the middle of the 12th century.