Canterbury Cathedral’s Great Drain

By Rod LeGear

In 1868, the Reverend E. V. Robert Willis, M.A. wrote a detailed paper on Canterbury Cathedral and the associated monastic buildings for the Kent Archaeological Society¹.

In the paper, he describes the monastic water supply and what has become known as ‘The Great Drain’, a surviving part of the Norman and Mediaeval drainage system.

In the 12th century, the energetic and enterprising Prior Wibert (1151-67), once described² as “farseeing, scientific, resourceful, and a man of boundless energy”, had a water supply piped into the precincts from springs north of the city. Wastewater was collected from the monastic buildings via an underground drain that discharged into the town ditch. Two pipes on the north side of the Cathedral conducted roof run-off water, which was also used to flush through the Necessarium before emptying into the drain.

Fig 1: Route of the Great Drain

A beautiful mediaeval illustration drawn around 1150 shows the layout of the water pipes and drainage system at that time and is represented in Willis’ paper (pp 196-197).

Between 1390 and 1411, Prior Chillenden made extensive repairs to the system, and later, Prior Goldstone (1495–1517) extended the drain around the east and south of the Cathedral to deal with flooding of the crypt. Of this new section constructed of Tudor brickwork, Willis writes:

Fig 2: Medieval illustration of water supply and drain layout after Wibert’s innovations

Prior Goldstone constructed a subterranean aqueduct outside the church on the south side, and close to it, with bricks and cement vaulted and firmly constructed, to carry off the inundations of rainwater which, for want of proper channels, were want to inundate the whole crypt of the Virgin and the adjacent chapels, and greatly hinder the access of the pilgrims to the glorious Virgin.

During its history, the drain has seen much maintenance over the years, reflected in the variety of repair materials that can be viewed underground, including brickwork, Ragstone and possibly Reigate stone, and in some parts, flint has also been employed. The walls in some sections north of the Cathedral contain blocks of a cream-coloured stone, possibly Caen or similar. In this part of the drain are small sections of older tunnels with vaulting constructed of squared chalk blocks. They may represent the surviving remains of Wibert’s original drain.

Goldstone’s section around the east and southeast of the Cathedral has had some of the vaulted brick roof removed at some point and replaced with what appears to be relatively modern paving slabs resting on iron supports (Fig 3).

Fig 3: Chalk block roof – possibly a surviving section of Wibert’s original drain – courtesy of Robert Hall KURG

Fig 4: Construction and repair materials – the modern pipe replaces damage by enemy action in 1940 – courtesy of Robert Hall KURG

Modern access into the drain is possible via several manholes placed along its route. Originally, the drain passed under the town wall to the north of the monastic site, and the water and effluent was emptied into the town ditch. This section under the wall has been replaced with a modern pipe, which takes the water to be released into a local authority drain, which eventually discharges into the River Stour. Several other access points to the drain once existed throughout the system and can be identified from below ground but have, in the past, been sealed and covered over on the surface (Fig 4).

Typically, the drain consists of a barrel-vaulted tunnel with an average width of 0.85m and a height which varies between 0.33m and 1.5m. Repairs and slight alterations can be seen throughout the system relating to maintenance and rebuilding over several centuries. The floor varies from modern concrete, stone slabs, or brick. Smaller, inactive drain tunnels and ancient and more modern pipes can be seen at various points, showing where the wastewater from the monastic buildings, including the infirmary, the Prior’s lodgings, etc., entered the main channel. In some areas, side tunnels have been blocked off with modern brickwork so that only the outline of the original opening remains. One section of the drain is now inaccessible as it was damaged by enemy action in 1942 during the Second World War and was replaced by a pipe.

Fig 5: Ancient pipework and possibly part of Wibert’s medieval water supply – courtesy of Hugh Farrer KURG

Fig 6: Typical drain profile – courtesy of Hugh Farrer KURG

Several lead pipes can be seen in the tunnels crossing the drain or along the wall. The larger, 3-inch (75mm) diameter ones are of considerable age and may be part of Prior Wibert’s original 12th- century water supply (Fig 5).

The Kent Underground Research Group (KURG)³, whose members have considerable experience working in cramped, restricted spaces, have been privileged to assist with inspection visits into the monastic drain on several occasions. Any visit into the drain must be well planned with extensive risk assessments, method statements and emergency evacuation procedures drawn up and adhered to. Lees Court Estate joined KURG in some inspections and kindly brought additional equipment (Fig 6).

Entering the drain is not for the faint-hearted or those who have claustrophobia, as most of the time it is hands and knees crawling. On the south side of the Cathedral, the width is 0.76m with a height of merely 0.69m. Even in the higher parts, an average person cannot stand upright as the height is only 1.20m. Adequate PPE is necessary for, as well as the usual hazards to be found underground, in an ancient drainage system, there are biological risks to contend with, such as Weil’s disease from infected rat urine. Although no rodents were encountered in the drain rat droppings, they were observed in several locations, indicating their presence.

Air quality safety tests were conducted before entering the tunnels, and oxygen levels constantly monitored. The air quality was excellent in most of the system. Strong draughts of air were noted coming from ceramic pipes let into the tops of the walls in the tunnels near the cathedral. It is presumed that these modern pipes now convey the run-off water from the roof. Several older openings for the same purpose could be seen, most blocked by soil debris after a metre or so, the more modern system having made them redundant and un-maintained.

Fig 7: KAS Patron Lady Sondes entering the drain – courtesy of Elizabeth Roberts LCE

Fig 8: Part of Goldstone’s extension on the south side of the Cathedral

In May 2016, KURG helped facilitate a trip into the drain to examine the structure by the Cathedral Director of Works and other interested parties, including KURG member and KAS Patron Countess Sondes. The following year, the Group were asked to help examine two sections of the drain to assess silt build-up in the drain passages. It was found that some of the silt buildup was caused by areas of root intrusion, which was slowing down the scouring effect of the water flow.

Fig 9: Safety briefing prior to descent – courtesy of Elizabeth Roberts LCE

In July 2017, KURG volunteers returned and carefully cut back and removed the offending root material, taking extreme care not to damage any brick or stonework.

The Great Drain is a fascinating hidden part of the history of the Cathedral site and, considering its age, is in excellent condition. Priors Wibert, Chillenden and Goldstone would be pleased to know that their construction is still used centuries later.

Fig 10: Checking oxygen levels before entering – courtesy of Mark Sharratt KURG

References

1 Reverend E. V. Robert Willis ‘The Architectural History of the Conventual Buildings of the Monastery of Christ Church Canterbury’ Arch. Cant. Vol. VII (1868) pp1-206 2 Margaret Babington Canterbury Cathedral J M Dent London 1933 3 The Kent Underground Research Group members are an eclectic mix of archaeologists, speleologists and those interested in the subterranean heritage of the county.
www.kurg.org.uk