Combe Down Stone Mines

Overview

A vast network of underground Bath stone workings beneath the village of Combe Down, developed by Ralph Allen from the 1720s to supply the stone that rebuilt Georgian Bath — later left so unstable by 19th-century pillar-robbing that Bath & North East Somerset Council spent ten years and over 400,000 cubic metres of foamed concrete backfilling the mines to save the houses above them.

History

Ralph Allen began buying land on Combe Down in 1726 and had acquired quarrying rights across the hill by 1729, developing what became four merging workings — Firs Quarry, Byfield Mine, Allotments Quarry and Coxe's Quarry — collectively known as Combe Down Quarry, eventually covering more than 10 hectares underground. Allen built a horse-drawn tramway down to the Kennet & Avon Canal to move stone into Bath, and used his own product to build Prior Park, Queen Square and the Royal Mineral Water Hospital, proving Bath stone's quality to the architects rebuilding the city. He also built De Montalt Place, a terrace of eleven cottages designed by John Wood the Elder, to house his quarrymen. After Allen's death in 1764 his heir, the Earl de Montalt, sold off the tramway and cranes and turned Combe Down into a health resort rather than continuing to work the stone commercially, though quarrying by smaller operators carried on into the 19th century. The mines were later used as an air-raid shelter during the Second World War. By the late 20th century, decades of unrecorded and often reckless extraction — stone quarrymen routinely 'robbing' the pillars left to support the roof — had left the workings dangerously unstable; when roof falls at Firs Quarry began causing subsidence above ground, a 1994 survey found some 80% of the underground workings had less than 6m of rock cover, in places as little as 2m, directly beneath occupied housing. Oxford Archaeology was called in to record the workings before a ten-year council stabilisation project (1999-2009) backfilled 25.6 hectares of mine with foamed concrete, protecting 649 properties above.

Geology

The mines work the fine-grained oolitic limestone known as Bath stone, part of the Great Oolite Group, quarried both as a building freestone and, at Combe Down, mined entirely underground rather than opened at the surface. Fracture patterns in the rock played a direct part in the site's later instability: where natural fractures ran parallel to the long axis of a mined chamber, a greater span of unsupported stone was left along the joint, making roof collapse more likely.

Workings

Stone was worked by the room-and-pillar ('pillar and stall') method — parallel chambers cut with hand saws and picks, leaving regularly spaced pillars of unmined stone to hold up the roof — with blocks hauled out along underground tramways to Allen's surface railway. Later working was far less disciplined than Allen's own operation: smaller 19th-century quarrymen frequently cut pillars back for extra stone, weakening the very supports the whole system depended on.

What remains

No public access to the underground workings, which are now almost entirely backfilled with foamed concrete; the stabilisation is considered permanent. The Museum of Bath Stone, opened in 2014 as the stabilisation project's legacy, tells the mines' story and is open to the public on a limited weekly schedule. The wider mine complex is a Site of Special Scientific Interest for its bat population — the constant temperature and darkness of the remaining voids provide winter hibernation roosts for greater and lesser horseshoe bats.

De Montalt Place, Ralph Allen's terrace of quarrymen's cottages, still stands above ground, along with scattered blocked and gated mine entrances around the village; almost everything underground is now sealed beneath concrete fill.

Abandoned workings can be dangerous — unstable ground, uncapped shafts, flooding and bad air are common even where a site looks safe from the surface. This entry describes history and general location only; it is not an access guide.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• A 1994 survey found around 80% of the underground workings had less than 6m of rock cover above them, as little as 2m in places, directly beneath the village; the resulting stabilisation project (1999-2009) backfilled 25.6 hectares of mine with foamed concrete to protect 649 properties. ¹
• James Cottle, a quarryman working for a later operator, was killed when a stone block set on edge toppled onto him after being struck by another stone being moved by crane — a single-fatality accident, not treated here as a qualifying mining disaster given the significance bar this site applies. ²
• The four merging workings that make up Combe Down Quarry — Firs Quarry, Byfield Mine, Allotments Quarry and Coxe's Quarry — together cover more than 10 hectares underground. ³

Sources

1. (secondary) The Stabilisation of Combe Down Stone Mines — Museum of Bath Stone
2. (secondary) Hollowed Ground: the archaeology of Bath's stone mines — The Past / Current Archaeology
3. (secondary) Building Bath with the best stone from Combe Down quarries — Prior to Now on Combe Down
4. (secondary) Combe Down and Bathampton Down Mines — Wikipedia
5. (secondary) Our story — Museum of Bath Stone

Record created: 21 August 2026 · Last researched: 21 August 2026