Aerial Archaeology: Roman Fort Castra Vetera I

Task: We will study the power of aerial photography and GIS for archeological prospection. The skills we will learn are

1. how to georeference images such as photographed or scanned maps as well as aerial photographs,
2. how to digitize elements from a georeferenced image.

Background: 2000 years ago the lower Rhine area played an important role in Roman history. The river was the border between the Roman empire (west of the Rhine) and ancient Germania (east of the Rhine). Much of the European history and its current way of life was strongly influenced by the Roman Empire and earlier the Greek and Middle East Empires.

North of modern Xanten was a major Roman city called Colonia Ulpia Traiana (CUT), which has been partly reconstructed. It is now the core of the Archaeological Park Xanten (APX).

South of modern Xanten, at the top of the Fürstenberg hill, was the important Roman castle Castra Vetera I. It was operated for several decades and modified several times. It is mainly known for its role in the Neronian phase, i.e. the times of emperor Nero up to 70 CE (CE: current epoque).

Roman Settlements in Modern Xanten Area

Fig. 1.1: Medieval Xanten, Colonia Ulpia Traiania and Vetera I (by P. A. Faulkner). Source: http://intarch.ac.uk/journal/issue17/4/4.html

Castra Vetera I and Colonia Ulpia Traiana
Fig. 2.1: Colonia Ulpia Traiana (by Dießenbacher Informationsmedien). Source: http://www.zeitreise-ruhr.de/chronik/060-roemerundgermanen.html	Fig. 2.2: Castra Vetera I (by Dießenbacher Informationsmedien). Source: http://www.zeitreise-ruhr.de/chronik/060-roemerundgermanen.html
Fig. 2.3: Vetera I, secured ground plan (by Dießenbacher Informationsmedien)	Fig. 2.4: Vetera I, reconstruction (by Dießenbacher Informationsmedien)
Fig. 2.5: Vetera I, Neronian fort, showing building numbers, kilns and fortifications of earlier forts (by P. A. Faulkner). Source and Legend: http://intarch.ac.uk/journal/issue17/4/4.html	Fig. 2.6: Source: http://www.roemisches-rheinland.com/Wissen/Festes-Lager

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Play with the interactive presentation The Xanten Area in Ancient Times: http://xanten.afg.hs-anhalt.de/desk30.html

Questions:

What was the Castra Vetera I and where was it located? Until when did it exist and what caused its abrupt end? Who were the Batavi? Which was their main settlement?

Interestingly you do not find any information about the location of Vetera I on recent topographic maps. Older editions do outline the approximate location of the castle. The map below indicate the castle's approximate location with a thin dashed line.

(DTK25: Deutsche Topographische Karte 1:25000):

Import the Web Mapping Services WMS of NRW into QGIS and use the official topograhic maps (TK… and Grundkarte) therein as a reference for the following tasks. To do so follow the instructions at Open Data NRW.

Use the georeference tool georeferencer to align the photographed map above with a current digital topographic map form open data NRW. Perform a non-linear transformation to georeference the map photo.

To georeference (= transform, correct) the photo I have taken from the topographic map a “Linear Transformation” is not appropriate. The image is mainly rotated (a non-linear transformation) and (linearly) distorted by perspective. The photo has not been taken perfectly orthogonally to the map plane. The transformation “Thin Plate Spline” does a good job. I cannot explain for now what it exactly is. The screenshot below shows the satisfying result after the non-linear transformation to correct the image. The locally different transformation of the image (dependent on the location on the image) are obvious. I do not know yet how to handle the black background of the rotated image on the vertically aligned rectangular canvas.

Use the georeferenced topographic map from 1998 to georeference the Vetera I reconstruction by Dießenbacher shown in Fig. 2.4.

Overlay these georeferenced maps / images on top of the DTM you created earlier (the geoTiff files generated from xyz). Is the reconstruction plausible?

The Ruhr-Universität Bochum has an Archaeology department by which several projects had been performed to investigate ancient Vetera I. Read the web page presenting results of aerial photography around Vetera I: http://www.ruhr-uni-bochum.de/archaeologie/forschung/projekte/luftbildxanten.html.en

Fig. 1: The gate of the Neronian encampment.	Fig.2: “Streifenhäuser” along the east leading road.	Fig. 3: Traces of the eastern breastwork of the camp.
Source: Baoquan Song (Ruhr-Uni Bochum), Norbert Hanel (Uni Köln): http://www.ruhr-uni-bochum.de/archaeologie/forschung/projekte/luftbildxanten.html.en

Where are these features located on the Fürstenberg? Try to georeference them.

Map them in the context of the georeferenced topographic map you created before and the georeferenced Castra Vetera I model by Dießenbacher.

How does the information fit together?

• Revolt of the Batavi (Wikipedia)
• Conquest of Germania esp. Lower Rhine Area (Zeitreise Ruhr)