Bill Putnam tells how Prince Charles, when told of a Roman Aqueduct on the Duchy of Cornwall Estate at Dorchester, looked baffled – until he was told they weren’t all like the
Pont du Gard. “He must have been wondering why he hadn’t noticed it!”
Dorchester’s Roman Aqueduct was a much more modest affair than its famous counterpart in Provence, and is now largely lost to view – unless you know where and how to look (it's the level line on the hillside in the picture). But it was
9.5 miles long, and did serve an essential purpose for
Durnovaria (Roman Dorchester) - supplying water for, amongst other things, the Baths – that essential feature of Roman life.
We explored the Aqueduct during one of Dorset County Council’s
Archaeology Days, when local experts lead field visits to particularly interesting or mysterious sites. Roman remains are ‘proper’ traditional archaeology, and Bill is a retired archaeology lecturer from Bournemouth University – but the aqueduct itself is also a classic example of ‘industrial archaeology’ (IA), clearly showing that IA did not begin with the industrial revolution, and is not just about canals, railways and steam engines. So there (sorry, I get a bit excitable about this sort of thing).
Our expedition gathered at
Poundbury Camp not far from Prince Charles’ controversial ‘traditional’
village of the same name. The Camp, a smaller cousin to nearby
Maiden Castle is an Iron Age structure, hanging on the side of the River Frome valley just upstream of Dorchester. But the ‘rampart ditch’ (see pic) nearest the river isn’t Iron Age but Roman, and is the remains of the Aqueduct where it skirted the old camp before crossing its ditches (infilled by Roman engineers) and carrying on to the town.
Bill explained how this earthwork had puzzled archaeologists for decades, as it obviously continued, on a shallow gradient, well beyond the camp in both directions. At one time it was described as an ancient cattle track(pic shows us walking the 'cattle track'). But around 1900 a Major Coates identified it as an aqueduct, with a course following the contours for many miles until a suitable clear-water stream was crossed (the river would have been too silt-laden and uncontrollable for the specialist uses the Romans needed).
Bill’s research and digs over many years (written up for the
Dorset NH&A Society and soon to be available via
Tempus books, but summarised
here) have suggested that the aqueduct structure, built cAD50, was a covered wooden box-shaped conduit (see pic, from weathered signboard) set in clay. This makes a lot of sense – reducing siltation and livestock pollution by eliminating groundwater flows from the hillsides above, and reducing the effects of weathering and erosion. It may not seem as romantic as an open water channel but it does fit closely with similar more modern constructions – such as the 19th century
Elan Valley Aqueduct (effectively just a big pipe) that carries water from Welsh reservoirs to Birmingham.
Moving upstream (very gradually) we come to Fordington Bottom, a dry valley at the western end of the Camp. Here the ‘low budget’ nature of the construction becomes more obvious – Pont du Gard would march straight across the valley on masonry arches (and its remains would have been noticed by the PoW), but Dorchester’s Aqueduct is more subtle – it stays on the level and goes the long way round on the valley sides (see pic of map - the aqueduct is shown on both sides of the valley). In this it is strongly reminiscent of medieval and later mill leats and the mid 18th century ‘
contour canals’ built by
Brindley.
Dropping down into and across Fordington Bottom, we were shown one of the key mysteries of the aqueduct. Here, where the line hasn’t been ploughed, and so is more than just a notch on the hillside, it takes the form of a large ditch – much bigger than that needed by the buried wooden conduit. And excavations indicate that the wooden conduit and its clay setting, was dug out c AD150 and now randomly forms the bank of the ditch. The ditch itself, though it looks like a water channel, is much too large, and is unlined – any water in it would rapidly drain into the chalk rock beneath.
So what happened here (and some distance up and downstream)? Bill has a theory that this is an unfinished rebuild – with the aqueduct structure ripped out to make way for a more solid masonry channel – which for some reason was never built. Possibilities include financial failure (civil engineering probably went over budget in those days too), a reduced need (other sources used in town – perhaps bucket chains (see a Time Team account of one in London
here) for the Baths, or a massive structural failure elsewhere on the aqueduct route (more on this below).
On we go to the source… There are lots of us – I estimate 50 and Bill was only expecting 10 – and our convoy of 20 or so cars causes minor chaos in the lanes. The final stop is the feeder reservoir site, and we lose a few stragglers en route – those at the back of the convoy must have missed the last turning. Whoops.
The source /start/ feeder/ reservoir is at
Frampton with parking at a tiny car park (which we overwhelm) at Tibb’s Hollow. A path through the woods here is enticingly labelled Roman Aqueduct but most will be sadly disappointed on arrival, as there’s nothing to see except an interpretation board and a dried-up stream.
It’s a different matter if you’ve got Bill with you of course. He explains that the dam, presumed of soil and rock construction, was lost ‘sometime in the past’ and that there is archaeological evidence of unusually thick soil just below it and 1.5 m thick sediment deposits in the formerly flooded areas above. There is no historic documentation for the dam, and so there is a possibility that it collapsed in Roman times, giving a plausible reason for the abandonment of the aqueduct improvement works downstream. But that’s pure speculation – like so much in archaeology.
Archaeological (and levels) evidence also suggests that the aqueduct was fed from the top, not the bottom of the dam – which would mean this was not so much a reservoir, more a settling lagoon, to reduce the silt load and ensure only clean water was carried into the aqueduct conduit. There is additional evidence here for a small garrison, dated AD50, presumably army engineers involved in construction, and of small quarries, presumably for structural materials.
And, er, that’s it. A Roman Aqueduct in Dorset; operating from cAD50 to 150; a very satisfying and speculative afternoon outing, and a refreshing change from the (relative) certainty of 18th/19th/20th century IA.
