Colchester’s Town Wall is the earliest and one of the most complete town wall circuits surviving from Roman Britain, dated to c.AD 65-80. The Wall was constructed in a calcareous mudstone, septaria, imported from an outcrop near Harwich, supplemented by courses of brick.  Nearly two thirds of the wall circuit still exists with the remainder surviving as buried archaeological remains; originally the Wall formed a circuit 2.8km long and 2.4m thick, and enclosed a rectangular area of 48ha.  Six gates were built in the Wall and internal rectangular towers were constructed on the inside of the Wall; today, there are the upstanding remains of only two gates, the Balkerne Gate and Duncan’s Gate. 

A large defensive ditch, over 5m wide and 3m deep, was dug around the outer foot of the Wall, around the same time as the construction of the Wall. This ditch was subsequently recut and enlarged in c.AD 275. An interior rampart was also added to the Wall in the mid-2nd century AD.

The Wall was repaired and refurbished in AD 917 by Edward the Elder. A substantial ditch was cut along the south side of the Wall in the late 10th or 11th century, 7.5m wide and  3.0m deep. An extensive programme of repairs was carried out in the 14th century and eight bastions were added along the south-east circuit. One of the best preserved bastions, Bastion 5, is today situated in Priory Street car park. The Civil War was the last military action seen by the Town Wall.

Unlike many other town walls, subsequent alterations have not altered the essential character of the circuit and it continues to define the historic centre of the town. It is one of the most important historic features and visual reminders of the Roman town, as most of the Roman evidence is buried deep underground.

In 2019, Colchester Borough Council adopted a new management plan.  The plan sets out a framework for the maintenance, enhancement, interpretation, presentation and celebration of the Town Wall and its setting. 

This Norman keep known as Colchester Castle was built around AD 1078 on the foundations of the Roman Temple of Claudius. It was built in at least two main phases and its initial form consisted of a single-storey stone keep with crenellated parapet wall. During the early 12th century, the keep's outer walls were raised by at least one storey and a fore-building was added on the south side to protect the main entrance. A barbican replaced this in the 13th century. The castle's earthwork defences consisted of an upper and 'nether' or lower bailey bank and ditch (to the north, and down-slope to the town wall) with at least one entrance in the upper bailey's south-west corner. The upper bailey defences had been built by 1101. The northern and eastern arms of the upper bailey defences survive as landscaped earthworks within Castle Park. The southern arms lies just to the north of the High Street, and the western arm, below or just to the east of Maidenburgh Street. The nether bailey is possibly part of a second phase, of the late 12th century. The southern end of the eastern arm of the nether bailey survives as a landscaped ditch in Castle Park. The western arm lies below or just to the east of Maidenburgh Street. A masonry chapel and domestic buildings stood to the south of the keep. The keep was partially demolished in the 17th century.

Colchester Castle is now home to Colchester Castle Museum where visitors can explore the Roman vaults and visit the roof of the castle for panoramic views around the town. The museum's collections focus on the history of Colchester and include many very significant finds such as the Kelvedon Warrior and the 'Fenwick hoard', a collection of Roman jewellery found under the Fenwick store on High Street, Colchester.