In the late 1920s, after the excavation of Windmill Hill and other sites, it became apparent that causewayed enclosures were a characteristic monument of the Neolithic period.

The hilltop also contains the remains of a Romano-British settlement on an adjoining smaller area called the plateau enclosure, along with some evidence of occupation in the 17th century.

An Anglo-Saxon sword was found in the smaller enclosure, and there is evidence of an intense fire in the same area, which implies a violent end to the Romano-British occupation of the hilltop.

The main archaeological site at Knap Hill is a causewayed enclosure,[2] a form of earthwork which began to be constructed in England in the early Neolithic, from about 3700 BC.

There is also evidence that they played a role in funeral rites: material such as food, pottery, and human remains were deliberately deposited in the ditches.

[9] They were constructed in a short time, which implies significant organization since substantial labour would have been required, for clearing the land, preparing trees for use as posts or palisades, and digging the ditches.

[13] Over seventy are known in the British Isles,[5] and they are one of the most common types of early Neolithic site in western Europe, with about a thousand known in all.

[30] A bank, with a ditch on either side, runs from the south-eastern corner of the causewayed enclosure down the hill, which is too steep for this to have been a pathway.

[34] The archaeologist Roger Mercer considered Knap Hill to be "the most striking of all causewayed enclosures", and recommended viewing it from the road to the west that runs from Marlborough to Alton Priors.

[36] Knap Hill was first mentioned as being of antiquarian interest in 1680, by John Aubrey, who described it as "a small Roman camp above Alton".

The barrow outside the enclosure, which lay to the south-west, was about a foot (30 cm) high and Thurnam found nothing there but some animal bones near the surface.

The first summer's investigation revealed the segmented nature of the earthworks, and led to the publication of a short note by Maud Cunnington in the journal Man in 1909, in which she asked readers of the journal to suggest explanations:[40] Recent excavations [at] Knap Hill Camp in Wiltshire revealed a feature which, if intentional, appears to be a method of defence hitherto unobserved in prehistoric fortifications in Britain...

It has been suggested ... that the work of fortifications was never finished, [but there is] considerable evidence in favour of these causeways being an intentional feature of the original design of the camp...

[4][note 3] By the time the second summer's work had been completed, every causeway had been excavated sufficiently to prove that the ditches ended where they appeared to from what could be seen of them above ground.

[46][47] The Cunningtons found several flint-knapping clusters, including one group of seventy-two flint chips six feet (1.8 m) deep in the ditch.

[29][47] The ditch and low rampart that surrounded the enclosure were mostly undetectable on the surface; the Cunningtons cut sections around the perimeter at intervals to confirm their path.

These had been dug from the ground level before the bank was raised, and were both circular, about two feet (60 cm) deep, and 3.5 to 4 ft (1.1–1.2 m) in diameter.

These contained flint flakes, coarse pottery and some animal bones, and Cunnington concluded that they were contemporary with the old enclosure and that it was a coincidence the long bank was raised over them.

A round fire hole was found under the circular mound, containing wood ash and pottery, some of which Cunnington identified as Roman.

Cunnington suggested that the fireplace must have been unusable once the quern was in it, and that this, along with the presence of the sword and the evidence of intense heat, implied a violent end to the occupation of the enclosure.

[42] Between the long bank and the dais were the remains of a small building (marked E on the plan), 23 by 13.5 ft (7.0 by 4.1 m), with walls made of blocks of chalk.

The ruins of another rectangular building (F on the plan) were found against the eastern side of the plateau enclosure's bank, with both Roman and 17th-century pottery sherds in the walls and under the foundations.

[53] Two low banks were found, running down the hill: one from the two ditches marked S on the plan, and one on the other side of the enclosure, leading down from one of the causeways on the north-western edge.

[58] Connah also found some Romano-British pottery in his cuttings, including four Samian sherds, one of which could be dated to the late 1st century AD.

Some later medieval pottery fragments were found in the upper layers of the cuttings, all of which may have originally been part of a single vessel.

Connah concluded that the skeleton probably dated to the Roman-British occupation, and that the Neolithic ditch was simply an area of conveniently soft ground for the burial.

[32][33] In 2011, the Gathering Time project published the results of a programme to reanalyse the radiocarbon dates of nearly 40 causewayed enclosures, using Bayesian analysis.