LIDAR Map of Exton and the Roman Grid

With work to be undertaken on Shavards Farm a map has been constructed from the LIDAR on which the image of the potential Grid of a Roman settlement was detected (Ref 1). This map is available to download by the various groups interested in the site. It is of one OS Grid square at 1 : 5,000, and this scale is accurately represented by the two dots at the NE and SE corners (20cms). It would be possible to provide a file for a larger scale if printers are available. The colour scheme refers to the different LIDAR prints on which features show discussed in Ref 2, which also discusses the need for confirmation evidence from different media. This is shown in the second map at the end of this report, which gives ground and air photo evidence.

Problems and issues of what LIDAR is picking up are discussed in Ref 3. The LIDAR map is made from the dark lines on the print. If the map is used to measure things on the ground you need a copy of the LIDAR print as light lines may also be forming features (copies will not be so accurate in scale as the image set up on the Web - but should be OK for measuring nearby features). Shavards Farm buildings are shown in the NE corner of the map.

Two Principal Grid Lines at almost N - S and E - W show as light lines bounded by dark lines, only the dark lines are shown on the above map. The Principal N - S has these lines 10m apart, and the E - W at 8m apart. The N - S is also followed by an air photo light line which continues N off the map but ends by the high status Roman building found in 1980 - 90s excavation. To the west of the A32 the Principal E - W becomes a huge causeway until it is truncated by the old course of r Meon - which is indicated by the dark line there -- it is also a parish boundary. It is assumed this causeway originally continued across the flood plain with intermittent LIDAR evidence.

Other less distinct E - W Grid lines can be seen on the LIDAR. One is close to the Principal E - W, and is not seen across the flood plain. Three others are similar to the Principal E - W in being light lines bounded by darkt lines 8m apart - only the light lines are shown on the above map as dashed lines. The southern line actually runs on the causeway, and shows some LIDAR evidence over part of the flood plain. So does the Grid line north of it - this has been detected by excavation beside the A32 as rammed chalk with Roman pottery built up 20cms above the natural chalk, with a large amount of crushed flint and Roman pottery above. Its width coincides with the 8m spaced dark lines. The Northern Grid Line goes all the way across the flood plain to the modern course of the river - and is followed all the way by air photography. Possibly this is another Principal E - W. There may be more grid lines to the north - we have only obtained LIDAR in the one OS Grid Square.

Roman Lanes

Crossing the site at an angle to the Grid Lines are three Roman Lanes, shown in Red. The two northern ones we are excavating on the other side of the river. The southern lane is visible as a terrace through a field on the W edge of the LIDAR print, and the LIDAR line points directly to this position. The LIDAR Lines are similar to the Grid Lines, and only the central light lines are shown. The two northern lanes continue on the southern slopes of Old Winchester Hill.

The Chichester Roman Road forms three lanes, with a 40' terrace, and two smaller terraces often on either side (but not always). But it has been found that the 40' lane takes a completely different route onto high ground of Teglease Down. The LIDAR was obtained to try and find how it crossed the flood plain. This results in the green and yellow markings by the lettering A32, Ref 2 explains the procedure, leading to Stocks Lane being the route. Ref 2 gives evidence that this is a later route than the 3 lanes above. It follows also that the Principal N - S connects with and starts at this newer 40' route. This has a baring on dating the N - S & E - W Grid Lines - while its possible that any earlier settlement may be grouped alone the above 3 Roman Lanes. It looks possible that Shavards Lane is at right angles to these Roman Lanes - and so may have been a Roman Grid Line - which may be the cause of it forming a dog-leg to the north of the Farm. It is also possible that the Stocks Lane route is an example of a Roman bye-pass.

Map 2

Map 2 at the end of this report adds air photo and ground evidence.

The Figure 1 by the A32 at the north of the map is a Roman Road from the tower found recently just off the map to the northern Roman Lane. It shows clear escarpments closing with the ledge which runs just west of the A32.

The Figures 2 denote the area of surface scatter of Roman pottery. It does not seem to extend much south of the Principal E - W Grid Line. It may extend further north if the ground is clear.

The Letters DL represent Dark Lines on air photos and in the region of Letters OD Optical Ditches can be seen in binoculars. These represent the side ditches following the 40' lane along Stocks Lane.

The Figure 3 indicates where build-up can be observed, indicating that the southern boundary of Stocks Lane beyond the Railway is the southern edge of the Roman 40' lane. This agrees with the LIDAR markings by the A32 lettering, which represents the width of the Roman lane stonework still buried deep in the flood plain.

Air photos following Roman Grid Lines

Map 2 shows where air photo lines follow the Roman Grid Lines, in Black. Where no air photo line has been detected the original colouring occurs. Only the Grid Line just north of the Principal E - W has no detected air photo line. Thus the Principal N - S has a light line shown as a Black dashed line from Stocks Lane (the Roman 40' lane) and continues off the map to the north to the to the high status Roman building found in the 1980s - 90s. The Principal E - W also has a light line up to the A32, but not detected across the flood plain. However a binocular swelling has been observed as shown. Optical features are also visible to the east of the A32 as a large terrace and swelling broadly continuing the fragment of huge causeway to the west of A32. The Northern Grid Line is followed by a light air photo line all the way to the modern river. This Grid Line is not shown on the Ref 2 map - but mentioned in the text. The next Grid Line to the south has a light air photo line running to the A32 but not on the flood plain. The third Grid Line to the south only has the easterly part up to the Principal N - S followed by an air photo light line.

Air photos and the Roman Lanes

The three Roman Lanes showing on the LIDAR crossing the Grid Lines obliquely do not have air photos following them for much of their length, but corresponding light air photo lines are seen to the west and east. Across the flood plain the Northern Roman Lane is shown as a light line bounded by two dark lines - expected to be ditches. Attempts to find the northern ditch by excavation by the A32 has failed - one reason we can now see is that the Roman Road from the Tower will join the Northern Lane at this spot near the Figure 1. The middle Roman Lane light air photo line joins and overlaps the LIDAR light line for a short distance. It is now reckoned that the Southern Roman Lane is not represented on air photos due to the accuracy we know its course on the LIDAR Map. However it does show as a terrace climbing up from the flood plain on the northern edge of the huge causeway as shown on the Map below. Air photography is repeated on the eastern edge of the Map 2, which gives more detail than was possible in the Ref 2 map of the optical swellings which have been observed as ground evidence. Here again the Northern Roman Lane is bounded by dark air photo lines, while much of the space between them is a lighter line - possibly due to scattering of stonework by the plough - which is common for the route under Old Winchester Hill. The Southern Roman Lane is not represented by any media east of it meeting the Principal E - W Grid line - though its alignment would cause it to merge with the Middle Roman Lane by the Old Railway.

Richard Whaley

REFERENCES

1. Environment Agency, OS Grid square SU61 - 62, 20 - 21, Scale 1 : 5000, 2016

2. Exton towards Old Winchester Hill, NEHHAS Journal 8 No. 10. 2017 www.nehhas.org.uk/rrch10.htm,

3. Richard Whaley, What is LIDAR picking up?. NEHHAS FAB e - News forthcoming http://www.nehhas.org.uk/lidar0.htm