Archaeologist Simon Johnson and Helen Foggo, Planning Manager from David Wilson Homes, with a section of the aqueduct being lifted out of the ground. Courtesy David Wilson Homes

Archaeologists unearthing parts of an underground Roman aqueduct in Lincoln have found the first evidence that it was actually used, contrary to previous thinking.

The aqueduct, near Lincoln’s Nettleham Road, has been known about for centuries, and archaeological investigations of it were carried out in the 1950s and 70s, with no firm evidence for their ever carrying water being found. However, with the recent start of a housing development on the site, the time came for sections of the piping to be removed and studied thoroughly.

Excavations also revealed that a road thought to have been a Roman construction is in fact post-medieval.

Simon Johnson, principal archaeologist at Pre-Construct Archaeology, who carried out the work, explained that visible calcium deposits suggest the pipes did carry water.

“There’s been persistent questions over whether the aqueduct ever functioned,” he said. “We’ve got at least one section where there is furring around the full circumference, suggesting it was used. Who knows for how long? You’re looking at decades to produce that sort of deposit, I should think.”

The aqueduct – an ingenious piece of Roman engineering – is thought to have taken water from a spring known as Roaring Meg, about one kilometre north of the site. There are several theories about the pipes: they might have been up to ten miles long, and possibly fed public baths, or a header tank for further distribution.

The Roman plumbing system is constructed from a series of terracotta pipes surrounded with ‘Roman concrete’, a lime mortar mixed with brick dust and chips (opus sigininum). The sealed construction meant that theoretically, water could be pressurised and transported uphill.

Simon and Helen with part of the terracotta piping in the ground. Courtesy David Wilson Homes

“Lincoln’s Roman aqueduct is one of the most famous in Britain,” said Michael Jones, the city archaeologist for Lincoln, “but also the most problematic, since we are still trying to understand how and from where water was brought uphill to the Roman city.”

“Any new evidence such as this is a bonus, and will not only allow more people to enjoy its fascination but also specialist engineers to test its strength under pressure.”

The sections of aqueduct within the site are well preserved due to their strong construction, apart from some damage by tree root growth and in places where service trenches have been dug. A section of the aqueduct will now be offered to Lincoln museum The Collection for public display, and site developers David Wilson Homes (who also funded the archaeological work) are donating another piece to a local school.

It is hoped that one part of the aqueduct will be subject to further analysis to determine whether it would have been able to support a pressurised flow of water. The limescale deposits could also be analysed, though whether this will yield clues as to how long the aqueduct was used is not certain.

The excavation also threw up a surprise about the road on top of the Roman water system. It was accepted that the road was a Roman creation (simply due to its proximity to the aqueduct) but these are usually well constructed, with cambers and ditches. The one on the site turned out not to be like this, and featured noticeable wheel ruts. In addition, investigations found artefacts such as glazed pottery fragments that date the road to much later, with lots of 17th-19th century debris including horseshoes, a buckle and lead shot adding weight to the theory.

“The excavations have shown clearly that the wide road surface that sealed the aqueduct is relatively recent and might date to the time when the city was growing again in the 18th century,” said Michael. “For example, do the ruts indicate very heavy loads, perhaps stone being brought from nearby quarries?”

One further discovery made during the work, prior to 43 homes being built on the site, has been that the individual pipes of the aqueduct were joined by terracotta collars – similar to modern drains.

“What we were assuming was that the pipes slotted together, with male and female ends, but actually they were male fitted with collars – a bit like modern pipes,” said Simon. “It was an unusual thing, bizarre really!”