Canterbury was surrounded by a wall in Roman times. Traces survive here and there. A fragment of the Roman Queningate can be seen in the city wall opposite St. Augustine's Great Gate, and further up, nearer Burgate, the Roman foundation of the wall is visible.
The walls are mentioned in several Anglo-Saxon documents. In 1011 the Danes succeeded in breaking into the city, slaughtering the inhabitants, and tossing them over the walls.
It has not yet been established whether the Roman and Saxon walls ran altogether on the same line as the later medieval walls, but about 1100 A.D. the city fortifications included the same area as they did to the end of the 18th century.
There were six gates in use in medieval times:-Northgate, Burgate, Newingate, Ridingate, Worthgate and Westgate. Later another came into existence, Wincheap Gate. The walls were frequently rebuilt and reconstructed but never called upon to withstand any real siege after 1011, though the city represented an important strongpoint in the system of national defence.
The Royal government was always attentive to the condition of Canterbury's walls, and whenever they started to become ruinous a peremptory note from the Crown would order their restoration.
The continuation of Chaucer's Canterbury Tales tells how when the Pilgrims reached Canterbury the Knight took his son, the Squire, to view the City Walls.
Round 1800 wholesale destruction of the city's historical monuments was allowed to start, due mainly to street-widening programmes, and before it was arrested by an awakening interest a century ago in medieval antiquities, five of the city gates and half of the walls had gone.
The length of the wall was 1.5 miles. It was strengthened by 21 Watch Towers, most of which survive, though embedded in houses. Half of the wall itself still exists, the best visible stretches being at the Dane John and Broad Street. Much of the City Ditch is now built upon. This process was far advanced by the 17th century when it was lamented that the military value of the wall was thus nullified. Even in the 12th century a certain amount of squatting in the Ditch had taken place.
The City walls are of Roman origin and more than half the medieval circuit survives. They were remodelled in the late 14th century to enable the use of gunpowder weapons in their defence and in this respect are among the earliest examples in the country.
The Roman town wall of Durovernum was built towards the end of the 3rd century AD and had at least one internal tower. Traces of Roman gates are recorded at Queningate, Riding Gate and Worth Gate and recent archaeological excavations have increased knowledge of the Roman fabric. The medieval wall followed the same alignment, a roughly oval circuit c.3000 yards in circumference. The ditch is mentioned in the Domesday Book and the walls were said to be in reasonable repair in c.1140. Repairs were carried out by the Crown later in the 12th century and again c.1290-1320. In 1363 a commission of enquiry described the walls as mostly fallen through age and the ditches obstructed. Work of renewal began by 1378. Archbishop Sudbury had begun the entire rebuilding of the West Gate in 1380 and in the 1390’s work commenced on the towers flanking the River Stour.
The master mason/'architect', Henry Yevele, is recorded as having a role in the construction of the defences and it may be to him that the use of 'keyhole' gun-ports can be attributed. Newingate/St George's Gate was built in c.1470 and may have imitated the West Gate since it had two circular towers. Many of the wall towers were repaired in the 15th and 16th centuries.
Most of the west side of the circuit, however, was demolished in 1648. The River Stour towers and parts of Burgate and St. George's Gate were demolished in 1769-92.
A section of Roman city wall survives to a height of c.16 feet and is capped by a continuous row of intact crenellations. This can be seen in the north wall of the Church of St Mary, Northgate. Standing medieval walling, often to parapet level now exists on the north-east, east and south sides but the ditch has been almost entirely filled in and in parts given over to car parking. There were, according to Hasted (1797-1801), twenty-one mural towers and seventeen of these remain. The towers are predominantly square on the north-east, and half-round to the east and south-east with a battered plinth. They are principally built in flint with ashlar quoins. Most contain key-hole gun-ports, one in each face. The wall-walk passed through the towers at first floor level. The West Gate has twin ashlar-faced drum towers with eighteen 'key-hole' gun-ports on three levels in addition to the traditional defensive measures in the gate passage. The gatehouse remains to full height.
Canterbury City walls are among the best preserved in England even though about one third of the circuit has been demolished. Of particular importance is the survival of a stretch of the Roman city wall to full height. The West Gate has considerable historic value being among the first documented defensive structures in the country to have been designed with the deployment of gunpowder artillery in mind. The 'keyhole' gun-ports are well designed and coordinated. They are of a textbook quality.
The surviving lengths of city wall are generally in good condition. In the 1950’s there was a programme of rebuilding a long stretch of wall on the east side which favoured visual effect rather than accuracy. A number of gun-ports were also restored clumsily. The West Gate appears to be in good condition. East of the site of North Gate in St. Radegunds Street there has been a recent exposure of early walling. Some of the towers on this side of the city are also in an un-restored state.