The first defensive wall was built around London by the Romans around 200 AD, 150 years after Londinium was founded. For nearly 1500 years the City of London's growth was limited by its City Wall. It was made chiefly of Kentish ragstone and large Roman bricks, with rubble and mortar filling the centre. Red tiles were used at intervals to strengthen it, and these can still be seen in the sections that still remain today. It took ten years to build.

Although they were not there when the wall was first built, the City Wall ran between the sites of two landmarks - the Tower of London and Blackfriars railway station. It was nearly two miles in length - enclosing an area of 330 acres - and was between six and nine feet wide and about 20 feet high, incorporating the north and west side of an existing 12-acre Roman fort. There were large city gates at strategic points along the wall to allow traffic in and out of the City. It takes about an hour to walk its perimeter.

The remains of the original Roman wall are 14½ feet high, the level of the sentry walk (it would originally have been around 20 feet high). Most of the Roman wall was rebuilt in the early medieval period because it had decayed, so it eventually reached 35 feet as it was rebuilt, repaired and strengthened, and became known as the City Wall. The ground level has steadily risen, so that much of the remains of the wall are now underground.

In the 13th Century, a series of towers was added to the outside of the City Wall after a new defensive ditch was dug around the outside of the Wall to provide further defence. The ditch was six feet deep, and varied between nine and 15 feet wide. There were at least 20 towers, spaced, on average, about 200 feet apart, each able to accommodate catapult machines. Two of the towers survive, one at Barbican (or outer fortification of the City) that has lost only the top third and marks the north-west corner of the old defences at Barbican, and one incorporated into the Barber-Surgeons' Hall.

During peacetime the towers were occupied by hermits, or leased for a variety of uses. The tower at the Barbican may have been used for this purpose, as the hermitage of St James in the Wall was built nearby. A suburb grew up outside the wall around St Giles's church in early medieval times. The wall became the southern boundary of the churchyard, and survived until it was demolished in 1803 due to what appears to have been slum growth in the area. The tower became almost buried under earth as it was dumped to raise the level of the churchyard, but it was uncovered during the Barbican development during the 1960s.

By the 17th Century, the Wall was no longer needed for defence, and the City needed to expand. The ditch smelled bad because the residents had a habit of throwing in rubbish and dead dogs, so it was filled in and the area used for gardens. Most of the Wall was demolished in 1760, and the sections that survived did so because they were too difficult to tear down and became part of shops and warehouses and the foundations of houses. During the 20th Century, several sections have been uncovered during excavations and preserved.

The Line of the City Wall

The Wall retained its original course throughout the centuries of its existence, with the exception of a slight adjustment when the Dominicans (black friars) persuaded Edward I to move the wall to enclose their friary. Instead of going directly south to the Thames from Ludgate, it turned west first, and met the Thames at the mouth of the Fleet.

The City Wall started east of the City of London on the northern edge of the Tower of London moat with a postern gate. It was smaller than the City gates, and was intended for pedestrians. The gate was probably built shortly after the moat was dug in the in the 1270s, but its closeness to the moat meant that its foundations were undermined by the flow of water. It collapsed in 1440 and was rebuilt further north. The gate became derelict and was demolished in the 18th Century.

Please note, the names in this section are extant street names, or the names of the old gates.

• The Wall followed a line northwards slightly westwards of the Minories to Aldgate, to the left of St Boltolph's without Aldgate in St Boltolph's Street.

• It curved to north-west running between Bevis Marks and Houndsditch (a ditch beyond the wall, hounds comes from the habit that people had of dumping dead dogs in the ditch) to Bishopsgate, where it passes in front of St Boltolph's without Bishopsgate.

• It ran along the back of Wormwood Street and followed the road now known as London Wall to Moorgate, where it parted company from London Wall and continued in a straight line to Cripplegate.

• At this section it incorporates the north and west side of a 12-acre Roman fort¹. It turned sharply south, then left the line of the fort to turn west to meet Aldersgate, passed in front of St Boltoph's without Aldersgate on its way to Newgate.

• South to Ludgate, where it turns west along Pilgrim Street and then south again to follow New Bridge Street to what would have been the Fleet River which runs underground now, parallel to City Thameslink, and down to the junction with the Thames where it stops abruptly.

Fascinating Facts

St Boltolph is the English patron saint of travellers. There were originally four churches dedicated to him in London, and they were all located at the edge of the city near gates. Travellers would pray for a good journey on their way out of the City, or give thanks for a safe arrival. The churches were named St Boltolph without because they were outside the City Wall. The fourth church was at Billingsgate, which was destroyed in the Great Fire.

It is possible that the wall had a stretch along the waterfront (built in around 350AD), although it would not have lasted very long as the river frontage was gradually being extended and built on. While possibly not being gates in the City Wall, Billingsgate was one gateway into the City (meaning artificial port - it had been constructed on the bank to provide a crossing point for visiting dignitaries), the other Thames gate was Dowgate, which means water gate.