Modern-day Gloucester is built on (and in a few rare cases partly from) the Roman fort then colony of Glevum, established in the 1st century AD. The rectangular colony was enclosed by strong defensive walls with corners at the sites of today's Cathedral, north-east corner of King's Square, the junction of Brunswick Road and Parliament Street, and close to the bottom of Barbican Road. Gates were placed in the middle of each length of wall, and the main roads within the colony formed a cross between them (mostly – the road from the south gate was stopped short of the centre by a forum). The Romans commonly built outside colonial walls, and it is known that a significant riverside development was established beyond the west wall.

Although an important Roman centre – one of only three Roman colonies in early Roman Britain – Glevum was left to ruin after the Romans abandoned Britain in the early-5th century. When the Saxons, from whom the name Gloucester originates, re-established the site as a major centre in the 10th century, the few Roman structures still standing became mostly quarries and did not long survive.

During the Saxon period the main walls still stood, as did the Roman riverside quay wall in lower Westgate. The principal Roman streets – the four gates – also survived. Even then, Westgate Street was re-established on a new line slightly north of its Roman ancestor, through the colonnade of a pair of Roman public buildings, the ten metre (thirty foot) columns of which "survived for many centuries." Southgate Street too is slightly different from its Roman ancestor, having been extended by the Saxons through the site of the Roman forum to meet the other gate streets at The Cross. Other than the four gates, Gloucester's street pattern today is entirely Saxon and later.

There is evidence that part of a large 2nd-century Roman house located on the site of today's Ladybellegate Street car park opposite Blackfriars remained in use throughout the Saxon period (the area later became the 13th-century friary's cemetery). Whilst it's possible the Saxons maintained the Roman defences, the walls appear to have been substantially rebuilt soon after the Norman Conquest of 1066. Mostly.

It's not known exactly when – possibly late Saxon, possibly early Norman – but the west wall was the first of the city's old walls to disappear. Certainly, Saxon Gloucester extended beyond the west wall to the riverside, and the Norman abbey (later Gloucester Cathedral), construction of which began 1089, was built across the north-west corner of the old wall on the site of a late Saxon abbey, in an area where the early-Saxon king Osric had established an abbey in the 7th century (the exact location of which is not known).

The sequence of Norman castle building at Gloucester in the late-11th and early-12th centuries straddled the line of the Roman wall to the south-west, giving us the latest date for the demise of the west wall (the line of this length of Roman wall, now known to have run along today's Berkeley Street, was not accurately established by archaeologists until the 1970s).

The Roman quay walls were demolished in the 12th century, and even in medieval form what remained of the defensive wall lining the western half of Gloucester, from south gate round to north gate, became a source of raw material for other building works. By the time of the siege of Gloucester in 1643 during the English Civil War, only the eastern half of the city's ancient walls still stood. These were pulled down on the orders of a vengeful King Charles II in 1662.

What remains of Roman Glevum today lies almost entirely underground. Exceptions are found in Roman stone re-used in later buildings. The ruins of St. Oswald's Priory, whilst mainly 12th and 13th century, still contain some Roman stone recycled by Saxons during the original construction c.900 AD. Archaeological research has shown the Roman wall in the cathedral precinct to have been robbed, presumably for material to build the abbey, and stone in the south wall of the 12th-century west slype in the cathedral's Church House betrays Roman blockwork and tooling. There is evidence in the remains of the Cathedral infirmary that Roman buildings were still available as a source of building material as late as the 13th century, and the use in 15th-century work on the cathedral's nave of stone inscribed with a dedication to a cohort of the Roman 20th Legion indicates repeated re-use of recycled Roman stone.

Surfacing Glevum in the Modern Era

Numerous glimpses of long buried Glevum have been revealed in the modern era and, more importantly, recorded, albeit to varying degrees of accuracy and usefulness. A 1933 article titled Glevum, published by the Bristol and Gloucestershire Archaeological Society, summarises the then known Roman finds in and around Gloucester. With archaeology still in its infancy, the vast majority of information came from often archaeologically destructive building works over the previous century or so. The article is replete with reports of substantial Roman finds within the area of the Roman settlement at Gloucester, including sections of the defensive wall and remains of the walls and tessellated floors of Roman buildings. As archaeology became more established in the 20th century, the approach to Roman studies has become more scientific and better integrated with construction projects.

The first known columns of many found along Westgate Street were unearthed during building work in the late 1820s. A century and a half later, archaeologists shadowing the construction of the HSBC Bank at the top of Westgate Street in 1971 located another column, broken but still two metres (over six feet) high. It was the fifth such column uncovered by archaeologists which, alongside another seven known from historic sources, have established the existence of the Westgate Colonnade. The parallel line of columns lying buried either side of modern-day Westgate Street once belonged to two large Roman public buildings that stood on the north side of the Roman street between centre and west gate, and it was through this colonnade that the Saxons rerouted Westgate Street.

Building works in the first half of the 19th century on the now long since demolished gas works between Quay Street and the prison, and again in 1938 for the Co-op Creamery opposite the Church of St. Nicholas on lower Westgate Street, unearthed evidence of a Roman quay and possible harbour. Post-war archaeological excavations, including on the site of the Co-op Creamery when it was demolished in 1990, have definitively established the existence of the Roman quay along the east bank of the Severn, which during the Roman period ran along the line of today's Lower Quay Street, and added to the debate about the existence of a Roman port at Gloucester.

Workmen digging foundations in 1825 for a new nave at the 12th-century St. Mary de Lode uncovered a Roman tessellated pavement. An archaeological excavation on the same site in 1979 confirmed the mosaic to be part of a mid to late Roman temple or baths complex. The archaeologists also dug deeper to discover an earlier, late-1st or early-2nd century Roman building of high status.

In 2017, as part of a watching brief by Avon Archaeology during works conducted at St. Mary de Crypt, two large pieces of carved Roman stone dated to the late-1st or early-2nd century were recovered from a trench dug as part of new sewerage works. In what has been described as Gloucester's "most important discovery in decades," the stones are hypothesised to have been part of a Roman temple, possibly dedicated to Jupiter, that stood on or near the site of today's church. More recently, in a video produced in 2021 by Gloucester Civic Trust/The Folk of Gloucester, City Archaeologist Andrew Armstrong reports the find of Roman tower walls in the north-east corner of the Roman defensive perimeter at the King's Square redevelopment.

Whilst the King's Square walls will be resealed and left for future archaeologists, construction has often resulted in destruction of the Roman archaeological record, even in recent times. For example, the building in 1882 of the Co-op store along Queen Street, next to the site of the east gate on Eastgate Street, resulted in the removal of a portion of the buried Roman wall. Still more Roman wall was lost during structural alterations to the store in 1931, and when the Co-op building was replaced in 1980 by the current Boots store, what was left of the wall buried beneath Queen Street was destroyed (as was Queen Street itself, which became the covered passage now called Queen's Walk). To compensate, the Boots development installed a viewing chamber down onto the surviving remains of the east gate outside the store on Eastgate Street. Though the ruins on view are substantially post-Roman, parts of the Roman wall can be seen disappearing under the modern pavement at the west end of the viewing chamber, and guided tours of the chamber can be booked at the Museum of Gloucester.

There is one publicly visible Roman remnant above ground in Gloucester, located in the Furniture Exhibition Centre at the bottom of the pedestrian zone on Southgate Street. With permission from the store owner (freely and friendly given in my experience), it's possible to view a small stretch of the city's ancient wall, comprising both medieval and Roman stone.

The extent to which Roman Glevum lies buried is evident in the latest King's Square discovery. At the time of filming, only the tops of the walls had been uncovered, and that some two metres (more than six feet) below current ground level. Even that depth is considered unusually shallow for the majority of buried Glevum. It's likely that the base of the walls are some four metres (thirteen feet) below ground; excavations reported in 1982 and 1995 on Westgate Street inside and outside the Roman walls have located Roman levels at a little under four metres.

Some of the Roman mosaic still lying beneath St. Mary de Lode is on occasion open to public viewing, but the vast majority of Roman Glevum that can be viewed today comprises artefacts ranging in size from pottery fragments and coins to tombstones and pieces of wall, removed from the locations they were found and placed on display. Foundation stones of the Roman north gate recovered during construction work on Northgate Street in 1974 can be seen in the Longfield charity shop that currently occupies part of the building that went up during that construction.

The foundation piece of the Westgate column found in 1971 is currently on display in the HSBC window on Westgate Street, and the rest of the column is on display in the Museum of Gloucester. While the vast majority of Glevum remains coyly and, one hopes, safely buried, the museum, housed in a Victorian building erected on the line of the Roman wall on Brunswick Road, is the main repository for all things Roman that have been surfaced in Gloucester, including a substantial stretch of that wall.