The widespread implementation of GIS-based 3D topographical models has been a great aid in the development and testing of archaeological hypotheses. In this paper, a topographical reconstruction of the ancient city of Tarraco, the Roman capital of the Tarraconensis province, is presented. This model is based on topographical data obtained through archaeological excavations, old photographic documentation, georeferenced archive maps depicting the pre-modern city topography, modern detailed topographical maps and differential GPS measurements. The addition of the Roman urban architectural features to the model offers the possibility to test hypotheses concerning the ideological background manifested in the city shape. This is accomplished mainly through the use of 3D views from the main city accesses. These techniques ultimately demonstrate the ‘theatre-shaped’ layout of the city (to quote Vitrubius) as well as its southwest oriented architecture, whose monumental character was conceived to present a striking aspect to visitors, particularly those arriving from the sea

Fiz, Ignacio

Orengo, Hèctor A.

Propylaeum-DOK

 Modelling Movement and Perception 1
Hèctor A. Orengo – Ignacio Fiz
The Application of 3D Reconstruction Techniques in the Analysis 
of Ancient Tarraco’s Urban Topography
Abstract: The widespread implementation of GIS-based 3D topographical models has been a great aid in 
the development and testing of archaeological hypotheses. In this paper, a topographical reconstruction 
of the ancient city of Tarraco, the Roman capital of the Tarraconensis province, is presented. This model is 
based on topographical data obtained through archaeological excavations, old photographic documenta-
tion, georeferenced archive maps depicting the pre-modern city topography, modern detailed topographi-
cal maps and differential GPS measurements. The addition of the Roman urban architectural features to 
the model offers the possibility to test hypotheses concerning the ideological background manifested in 
the city shape. This is accomplished mainly through the use of 3D views from the main city accesses. These 
techniques ultimately demonstrate the ‘theatre-shaped’ layout of the city (to quote Vitrubius) as well as its 
southwest oriented architecture, whose monumental character was conceived to present a striking aspect to 
visitors, particularly those arriving from the sea.
Introduction
The implementation of GIS-based 3D topographical 
models has been a great aid in developing and test-
ing archaeological hypotheses. However, one of the 
most evident problems of these models is that, be-
ing constructed on the basis of modern topographic 
maps or on-site spot height measurements, they 
reflect modern topography that cannot reliably be 
extrapolated into past periods of time. The topog-
raphy of modern Tarragona has been largely devel-
oped as a result of the use of its maritime façade and 
neighbouring areas of quarries providing stone to 
build the 18th and 19th century port structures. This 
has changed the topography of the city drastically, 
rendering 3D models obtained through modern 
maps inadequate in the analysis of the Roman city 
layout.
The aim of this project is to develop a methodol-
ogy that allows the reconstruction of the abrupt re-
lief in which the ancient city of Tarraco was settled. 
In addition, an attempt will be made to determine 
to which degree topography influenced the distri-
bution of major public buildings. The topographical 
reconstruction of Roman Tarraco will be combined 
with various data sources to aid interpretation and 
facilitate the process of archaeological hypothesis 
generation.
Methodology
Different sources were employed to recreate the to-
pography of the ancient city; each of them providing 
different data not only in their form but also in the 
way in which they must be dealt with. These sources 
of evidence must be further differentiated according 
to the kind of reconstruction they allow us to make, 
whether coastline, archaeological elements, ancient 
spot heights or other elements.
Although this methodological approach is part 
of an ongoing project, enough information has been 
gathered to produce some firm preliminary results.
Initial ideas and data were obtained from Gabriel 
(2001) who also produced a topographical recon-
struction using analogical means from photographic 
evidence and old maps. The work by Fiz (2001) and 
Fiz / Macias (2004, 14–20) provided a methodologi-
cal framework and the initial GIS geodatabase from 
which this project developed.
Ancient Map Analysis
Analysis of old maps can provide important evi-
dence on the ancient coastline and may aid in the 
location of the ancient Roman harbour and other 
topographical and archaeological elements of the 
area.
2 Layers of Perception – CAA 2007
A set of twenty maps covering the last five centu-
ries were selected and scanned, maintaining a defi-
nition higher than 1 m/pixel in each case.
In order to introduce old maps into the GIS they 
have to be georeferenced. The significant landscape 
change that took place in the city since the 17th cen-
tury made it impossible to find appropriate ground 
control points (GCP) from which the oldest city 
maps could be georeferenced. A regressive georef-
erencing methodology had thus to be applied in 
order to overcome this problem. In practice GCPs 
were identified on modern maps from which 19th 
century maps were georeferenced. From those, 18th 
century maps were in turn georeferenced and, fi-
nally, from these it was possible to georeference the 
oldest maps available. The use of chronologically 
intermediate maps proved to be essential in order 
to relate modern maps to the oldest ones, ensur-
ing their correct geographical referencing. Root-
mean-square error (RMSE) values resulting from 
the georeferencing process were interpreted as an 
indication of the differential accuracy of the various 
maps.
Once the maps geodatabase was developed it al-
lowed the extraction of features of interest, mainly 
the ancient coastline and the Roman harbour, but 
also architectural elements, building plots, paths 
and channels. From the three ancient maps with 
lower RMSE values the coastline was extracted as 
a line feature (Fig. 1a), which was then transformed 
to point features (Fig. 1b) that were, in turn, interpo-
lated into a new mean line (Fig. 1c). In this way the 
mean coastline can be extrapolated from the more 
accurate ancient maps. Following a similar process 
the Roman harbour, still visible in the oldest maps, 
can also be relocated.
Analysis of Archive Photographs 
Analysis of old photographs allows approximate 
calculations of the ancient ground level. Many ref-
erence features with known height can be still em-
ployed to assign a height to lost ancient landmarks 
present in old photographs. Pictures dating back to 
the end of the 19th century testify the employment 
of Tarragona’s maritime façade as a quarry (Fig. 2). 
This was a fundamental process since it drastically 
modified not just the urban topography, but also 
the ancient coastline through the construction of the 
modern port. Spot heights, extracted from old pho-
tographs by Gabriel (2001), have been employed 
in the generation of the 3D model outlined in this 
study.
Archaeological Excavations
Archaeological excavations can provide extremely 
useful evidence for the reconstruction of ancient to-
pography. Roman ground levels are measured as a 
standard procedure in every excavation. The advan-
tages of this type of elevation data are many. Firstly, 
Fig. 1. Methodology followed in the process of obtaining 
a mean coastline.
Fig. 2. Old photographs showing major changes in the 
city shape.
 Modelling Movement and Perception 3
they are the only source, together with standing 
archaeological features, that provides ground level 
measurements for the study period. Secondly, their 
accuracy is much higher than that obtained from old 
photograph or ancient map analysis, being second 
only to GPS measurements. Finally, Roman ground 
levels can be easily and securely extrapolated, par-
ticularly in the case of large plane extensions, such 
as the provincial forum or the city circus. However, 
this method is not flawless as it is impossible to test, 
considering that the evidence has been destroyed 
and, in many cases, ground level is measured in re-
lation to other features or to arbitrary base points, 
which complicates the calculation of global spot 
heights.
Standing Archaeological Features 
Standing archaeological features are plentiful in 
modern Tarragona. The theatre, amphitheatre, parts 
of the circus, parts of the provincial and city forum, 
the Roman city walls, and other features provide 
the same advantages as archaeological excavations, 
but can be also checked on site and, by means of 
differential GPS measurements, to offer high pre-
cision spot heights. These elements are particu-
larly useful since, being grand public works, their 
ground level can be extrapolated to large surfaces. 
It is indicative that in the case of the provincial fo-
rum the first level square covers 4–5 ha of levelled 
ground.
Preserved Ancient Bedrock
This information is more difficult to handle due to 
the problematic identification of undisturbed bed-
rock surfaces. These are typically located outside 
the walled city, forming strong gradients but their 
weathered appearance can often be deceptive. Old 
maps were employed to identify areas that have 
witnessed no major changes during the last three 
centuries. This temporal lapse is considered to be 
critical since it was the construction of the 19th cen-
tury and modern harbours that motivated the use 
of the maritime façade as a stone quarry. It is likely 
that surface bedrock areas occurring before 1792 
were also present in the Roman period (Gabriel 
2001).
Their correct location is important for the recon-
struction of suburban areas, primarily those facing 
the sea, which form an essential part in the re-crea-
tion of the city’s maritime façade.
Modern Topographical Maps
1 : 5000 scale maps with spot heights from the Car-
tographic Institute of Catalonia plus 1 : 500 City 
authority maps were employed to create a sur-
face from which interpolations could be drawn for 
those areas where no or insufficient evidence was 
available.
The Creation of a 3D Topographic 
Model of Roman Tarraco
Once all the elevation data was obtained a 3D mod-
el was created through the use of a triangulated ir-
regular network (TIN). This method was preferred 
because there was no interpolation involved and 
the data were kept without further modification. An 
additional advantage is that the TIN does not use 
many system resources and is easy to explore. The 
latter is an important aspect as the key aims of the 
model are for it to be flexible and easily updated as 
new information becomes available. With the clip-
ping of the reconstructed ancient coastline and the 
Roman harbour to the TIN the topographic model 
was completed.
Finally, archaeological information was intro-
duced into the model to allow an approximate 
view of the city in the Roman period. The sche-
matic reconstructions of the Roman buildings were 
created in a 3D CAD environment and exported 
in a GIS compatible format. Some of the build-
ings were easy to model as they were particularly 
well preserved. Nonetheless, most of the modelled 
buildings followed the plans published by Ma-
cias et al. (in press). The final result is presented in 
Fig. 3.
Fig. 3. 3D model including documented roads, the Ro-
man harbour, the ancient coastline and archaeological 
features.
4 Layers of Perception – CAA 2007
Fig. 4. Fragment from Wyngaerde’s painting showing the ancient walls (from Remola 2004, 69, Fig 16).
Proposed Analysis: 
3D GIS-based Visual Analysis
3D GIS offers new visualization possibilities that can 
go beyond the simple generation of raster viewsheds. 
In this section an attempt will be made to utilize 
meaningfully the possibilities offered by the model. 
Traditionally, pictures, drawings or engravings have 
been left out of any GIS geodatabases. However, they 
provide a great amount of information since they 
depict landscapes as seen in a given moment from 
a given location. Some of those artistic representa-
tions can be very old landscape views; an important 
precedent of aerial views and modern maps. This is 
the case in one of the most representative drawings 
of Tarragona: Van den Wyngaerde’s view of Tarra-
gona from the tower of Saint Fructuós Church, 1563. 
This drawing depicts elements of historical interest 
that no longer exist and have not been located by 
modern archaeological research, the most important 
of which is a stretch of the Roman city walls (Fig. 4). 
As a result of the previous process of ancient maps 
geore ferencing it was possible to locate accurately 
Saint Fructuós Church tower, as it appears in a map 
from 1641. Other elements appearing in Wyngaerde’s 
drawing were also located in the georeferenced 
maps.
The 3D model allowed the generation of 3D 
views from the exact point from which Wyngaerde 
produced the drawing, using the model to recreate 
the landscape as seen by the artist (Fig. 5a). The 3D 
views were oriented towards those elements ac-
curately located in old maps or still existent in the 
landscape that corresponded with elements from 
the painting. These views can be then employed as 
a test field where lost historical features still present 
in the drawing may be relocated. In this case it was 
possible to estimate the location of that lost stretch 
of the Roman city walls present in Wyngaerde’s 
drawing (Fig. 5b).
It is also possible through the use of 3D views to 
test hypotheses relating to urban topography and the 
distribution of public buildings. A series of 3D views 
were developed from the various documented city 
entrances and the roads leading to these entrances. 
None of these showed a comprehensive view of 
the city and its monuments. Many public buildings 
were hidden by the topography or by other archi-
tectural features, mainly the city walls. Finally, a 3D 
view of the city from the port was generated and it 
was immediately evident that from this location it 
was possible to see all the important public build-
ings apart from the amphitheatre (Fig. 6). There is 
a strong suggestion that the city developed visu-
 Modelling Movement and Perception 5
ally from this location, with the distinctive terraced 
architecture designed to maximise visual impact 
with respect to this approach. This 3D view clearly 
shows how the topographical setting of Tarraco’s 
public buildings was conceived to be seen from the 
harbour, arguably the city’s main “gate”, following 
Hellenistic concepts typical of terraced cities, such 
as Pergamon. Vitruvius (II, 8, 11), referring to Hali-
carnasus, states that ‘Is autem locus est theatri curvatu-
rae similis’1 while Diodorus (XIX 45.3 and XX 83.2) 
uses the same term to describe the city of Rhodes. 
These classic authors were comparing the shape of 
Halicarnasus and Rhodes with a theatre – a descrip-
tion that would also be applicable to Tarraco. 
This theory has been previously outlined by Mar 
(1993, 107) and Ruiz de Arbulo (1998), who have 
highlighted the levelling of the hillside through rock 
cuttings, terracing walls and soil movements in or-
der to keep a superimposed axial view of the city, 
with the main temple on top of it. Ruiz de Arbulo 
has also stressed the imposing view of the city when 
arriving from the sea.
A cumulative viewshed was developed to test 
this hypothesis. 33 view points were distributed 
along the path a ship would follow when approach-
ing the city from the Northeast. The results (Fig. 7) 
show that the view from the ship encompasses only 
the cliffs of the maritime facade and the city walls. 
When the ship reaches the harbour the view sud-
denly expands to include most of the city area in-
cluding all those public buildings inside the city 
walls. Thus, it is clear that the sudden appearance 
of the city in all its magnificence to the people ar-
riving from the sea was designed to maximise the 
visual impact of its monumental stratified architec-
ture. The maritime southwest approach would not 
be that magnificent, nevertheless, this trajectory is 
aligned with the viewing axis of the city and, con-
sequently, it would have allowed the gradual emer-
gence of the city’s façade.
Conclusions
While the methods and results presented here are 
only preliminary, some significant conclusions can 
be drawn. Although 3D models have been widely 
used within GIS-based archaeological analysis, the 
methodology presented in this paper, combining 
multiple lines of evidence, allows a better recon-
struction of ancient topographic settings with a 
Fig. 5. 3D views from the tower of Saint Fructuós Church 
orientated as in Fig. 4.
Fig. 6. 3D view from the roman harbour, showing the 
city’s main public buildings.
1 This other place is similar in its shape to a theater’s bend.
Fig. 7. Cumulative viewshed from the path a ship would 
follow when approaching the city from the northeast.
6 Layers of Perception – CAA 2007
higher degree of accuracy. In particular, 3D models 
have been employed here to allow the generation 
of positioned and oriented 3D views with the incor-
poration of pictorial data, so often ignored by GIS 
users, by comparative means. Thus, with the aid 
of a series of known reference points in the artistic 
representation and the place from which it was pro-
duced, it was possible to virtually relocate lost fea-
tures of archaeological interest.
This analysis demonstrates that the combination 
of the topographic model with 3D reconstructions 
of known architectural features is not only useful in 
the analysis of the distribution of the city’s public 
buildings and their relation to topographical set-
tings, but also contributes to the understanding of 
the ideological concepts underlying city planning.
Acknowledgements
The authors would like to gratefully acknowledge 
Ana Ejarque and Dr. Mark Gillings who have con-
tributed to improve this paper with their sharp com-
ments.
References
Fiz 2001
I. Fiz, Usos de un SIG, Sistema de Información Geográ-
fico, en la construcción de una Planimetría Arqueológi-
ca para Tarragona (I). Revista d’Arqueológia de Ponent 
11/12, 2001, 111–121.
Fiz / Macias 2004
I. Fiz / J. Macias, El port modern i la nova població de 
la marina. In: J. Macias (ed.), Les termes publiques de 
l’àrea portuària de Tàrraco: Carrer Sant Miquel de Tar-
ragona (Tarragona 2004) 13–20.
Gabriel 2001
R. Gabriel, Aproximació a la topografia antiga de Tar-
ragona. Bulletí arqueològic 23, 2001, 281–346.
Macias et al. in press
J. Macias / I. Fiz / L. Piñol / M. Miro / J. Guitart, Pla-
nimetria Arqueológica de Tarragona (Tarragona in 
press).
Mars 1993
R. Mars, El Recicinto de Culto Imperial de Tárraco y la 
Arquitectura Flavia. Documents d’Arqueologia Clàs-
sica 1.
Remola 2004
J. Remola, Tarraco quanta fuit ipsa ruina docet. In: 
J. Ruiz de Arbulo (ed.), Simulacra Romae: Roma y las 
capitales provinciales del Occidente Europeo: estudios 
arqueológicos (Tarragona 2004) 49–72.
Ruiz de Arbulo 1998
J. Ruiz de Arbulo, Tarraco: escenografia del poder, ad-
ministración y justicia en una capital provincial romana 
(s. II a.c.-II d.c.). Empúries 51, 1998, 31–62.
Hèctor A. Orengo
Ignacio Fiz
Universitat Rovira i Virgili
Catalan Institute of Classical Archaeology
Pl. Rovellat, s/n. 
43003 Tarragona
Spain
horengo@icac.net
ifiz@icac.net


The application of 3D reconstruction techniques in the analysis of ancient Tarraco's urban topography

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The application of 3D reconstruction techniques in the analysis of ancient Tarraco's urban topography

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