The Past and the Future: Archaeology and Computer Science
In the last fifty years, the growing use of computer applications has become a main feature of the archaeological research . Since the ’90s, when computer science was oriented to the creation of work tools and solutions for the archive and management of quantitative data, to the development of virtual models and to the dissemination of knowledge, it quickly changed into a true theoretical approach to the problems of archaeology. It is now, indeed, able to influence the interpretation procedures and to revolutionize the language and contents of the study of the past . This new evidence introduced in several branches of the theoretical debate new scientific themes. There are different views about the integration of computers and archaeology. Digital archeology in the Anglo-Saxon cultural world  is considered as a computer approach to the modern cognitive archaeology. Archaeological computing , on the other hand, is a methodology for the elaboration of archaeological data via computer. Archaeological computer science  is devoted to the representation with computer applets of the cognitive procedures behind the interpretation of the archaeological data, and the more popular virtual archaeology (VA) , is the analysis of the procedures of management and representation of the archaeological evidence through computer graphic 3D techniques.
Recently to its research the development of new communicative approaches to archaeological contents through the use of interactive strategies has been added. The birth of the VA is not simply caused by the proliferation of 3D modeling techniques in many fields of the knowledge, but as a necessity to experience new systems to archive an overgrowing amount of data and to create the best medium to communicate those data with a visual language. From this point of view, the application of 3D reconstructions, obtained with different available techniques, became the core area of study of the VA in regard to the potential of cognitive interaction offered by a 3D model. In this way, virtuality turns into a a communication method even more effective if applied to particular fields, archaeological areas well preserved but not accessible , sites not preserved but known by traditional documentations , sites destroyed but depicted in iconographical repertoires , contextualization in progressive dimensional scale (object, context, site, landscape), and functional simulations repeating in virtual environment the processes of the experimental archaeology.
From the Field to the Screen: 3D Computer Graphics and the Archaeological Heritage
The cognitive experiences of 3D computer graphics can essentially be divided into passive and active forms of interaction. The first case refers mainly to applications related to research and study, where the primary need is of documentary type, as the archaeological excavation or the monitoring of the degradation. In the second case, the interaction with the virtual recreated reality is further exploited in the enhancement of the archaeological heritage through the creation of a virtual museum, reachable on digital media or on the web, intended both as a virtual version of a proper museum and as a closer study of an archaeological site. Different is the case of the 3D reconstructions, developed within interdisciplinary research projects, made for the purpose of interpretation as a cognitive accessory available to the archaeologists.
3D Computer Graphics and the Archaeological Fieldwork
The other major field of application of 3D computer graphics in the world of archeology is the documentation of the excavation data in real time. Since archeology is the science of destruction par excellence, the need to document in a comprehensive and detailed way each item that is removed during excavation, imposed gradually the methods of graphic and photographic documentation in support of traditional 3D modeling . This technique can be used both for recording singular evidence but also for the objects set inside a GIS system in which 3D data are fully integrated. From this point of view the combination of GIS systems in archaeology and the development of 3D laser scanning and image-based 3D modeling techniques determined the birth of experimental systems of 3D GIS. This system is able to visualize inside the geographic information system 3D data, such as point clouds from laser scanners, and it has already produced excellent results as demonstrated in the case of Miranduolo excavation (Siena) Italy  or in the investigations in the Jabal Hamrat Fidan region of the Faynan District in Southern Jordan , just to name a few recent examples. The point of the application of these techniques on the excavation activity is the possibility to perform analysis on multidimensional scale. At landscape scales, digital 3D modeling and data analysis allow archaeologists to integrate, without breaks, different archaeological features and physical context in order to better document the area. At monument/site scale, 3D techniques can give accurate measurements and objective documentation as well as a new aspect from a different point of view. At artifact scale, 3D modeling allows the reproduction of accurate digital/physical replicas of every artifact that can be studied, measured and displayed, as well as data for general public use, virtual restoration, and conservation.
Monitoring the Heritage
3D modeling could also be extremely useful for the identification, monitoring, conservation, restoration, and promotion of archaeological goods. The archaeological heritage is always under constant threat and danger. Architectural structures and cultural and natural sites are exposed to pollution, tourists, and wars, as well as environmental disasters such as earthquakes, floods, or climatic changes. Hidden aspects of our cultural heritage are also affected by agriculture, changes in agricultural regimes due to economic progress, mining, gravel extraction, construction of infrastructure, and the expansion of industrial areas. In this context, 3D computer graphics can support archaeology and the politics of cultural heritage by offering scholars a “sixth sense” for understanding the traces of the past, as it allow us to experience it . 3D documentation of still existing archaeological remains or building elements is an important part of collecting the necessary sources for a virtual archaeology project. New developments allow this documentation phase, including the obtaining of correct measures and ground plans from photography using freely available tools. This is important when restoring archaeological remains, when older phases are reconstructed in a virtual way. The original state, the restored state, and eventual in between states can be recorded easily through this photo modeling technique . Furthermore, the recent application of 3D computer graphics has proved crucial in planning strategies of restoration and conservation issues of monuments that are part of world cultural heritage, on which there is still an open debate, as in the case of the restoration of the Parthenon on the Acropolis of Athens .
The Virtual Museum
The rapid development of 3D visualization techniques, and the subsequent derivation in the promotion policies for the archaeological heritage as well as the creation of 3D models of monuments and artifacts of past civilizations has become the basis for the birth of the concept of virtual museum as a means of transmission of knowledge based on the use of multimedia [17,18]. More recently, the seductive ability of visual communication, simplified and made more attractive by the opportunity to interact intuitively with multimedia content, has led to a huge proliferation of virtual museums on the web. The phenomenon in some cases has grown, losing sight of what are the ideological assumptions of the virtual museum itself. The virtual museum should not be considered as a transposition of a real museum in electronic form or on the web, nor can it be intended as a supplementary tool to complete the real museum, like a sort of exhibition space or additional digital catalog. Its nature is closely linked to its ultimate goal, namely to communicate knowledge to the wider audience possible, without stopping at generalizations between “scholars” and “public.” This aim is achieved with the use of communication strategies based on visual narratives, interactive multimedia narratives that tell the story of each artifact, contextualizing it geographically, historically, and culturally and embedding it into a network of information that goes beyond the artifact itself and what the real museum contains.
In this perspective, the virtual museum has its best expression in the version of the “museum of territory” which virtually took out of the museum’s closed walls the original cultural background of an entire territory. The virtual museum can also be considered as “a communicative projection of the real museum” which performs a dual function: educational, as it overlaps linguistical and physical barriers, and promotional, as it is also a tool of cultural exportation . Furthermore, the use of virtual reality and augmented reality technologies may make even more immersive and involving the experience of decoding the information. Just to cite an example of excellence in the most recent virtual museum project, it can be mentioned the Iraq Virtual Museum [8, 9, 20-22], completely accessible from the web, where the most advanced digital visualization techniques have been applied. It was promoted between 2006 and 2007, by the Italian National Research Council and the Italian Ministry of Foreign Affairs, as a concrete action for the cultural development of the Iraqi people through a targeted intervention for recovery of the Baghdad Museum intended as a shared treasure. Closed to the public in 1991, during the first Gulf War, and subjected to severe devastation and looting in 2003, during the turmoil of the second Gulf War, the Museum of Baghdad and its archaeological treasures, which covers 8,000 years of Mesopotamian history, were returned to the community only in February of 2009, thanks to the efforts of many countries.
3D Modeling as a Cognitive Tool
Computer graphics can be applied to the reconstruction and visualization of several features of an archaeological site with the creation of a multidimensional model including every feature derived from the excavations. This process is fundamental for scholars of virtual archaeology, the goal of which is the complete reconstruction of an ancient landscape. Computer science has a primary role in this branch of cognitive archaeology, and 3D modeling is not considered to be an optional implement for the addition of aesthetic elements in reconstructions, but an indispensable tool for interpretation. The available technologies and methodologies for the digital recording of archaeological sites and objects are promising, and the scientific community is trying to adapt these approaches for detailed 3D documentations to go beyond the simple graphic and photographic data. The process of interpretation of archaeological evidence, often fragmentary and subject to many variables of alteration, finds in 3D computer graphics a valuable experimental environment in which to test the reliability of the assumptions. Often what makes sense during a study about the nature and function of artifacts poorly preserved and stored in store boxes, can be completely changed by a simple passive observation of a 3D reconstruction, if not completely disavowed by interactive or immersive virtual models in which the man-space-artifact-building relation is recreated. From this point of view, the 3D computer graphics become on the same level of the archeology itself, as a digital version of the experimental archaeology [23-25], characterized by the study of the “practice supporting the theory” . It aims to the replication of experiments, the testing of methodological assumptions by applying them to known contexts, the experiments involving site formation processes. In the same way a similar research can be virtually conducted interacting with a 3D model replicating the reality. It is not a coincidence that in recent years several interdisciplinary projects of reconstructing the past have been completed thanks to the combination of the experiences both of experimental archaeology and 3D computer graphics . In this sense of cognitive tool, the use of 3D models in archaeological research can be intended as a sort of benchmark of what the perceptual senses and the mind perceived in the first instance. A sort of “seeing causes believing” opposed to a simple and sometimes misleading “seeing is believing” which is often altered by the cultural superstructure of the archaeologists . In this case digital technology is not only used to provide tools of discovery and communication but mostly interactive feedback . Just this aspect of computer graphics in archaeology is that privileged by the multidisciplinary research projects of digital archeology, which aim to bridge the linguistic and cultural gap that still divides the researchers of archaeology and computer science and to contribute to the common reconstruction of the past through its virtual experiencing.
The Archeomatica Project
A digital archaeology research project, directed by the authors, the Archeomatica Project  was begun in late 2007 by a group of prehistoric archaeologists and researchers in image processing and computer graphics from the image processing Lab , both of them of the University of Catania. It aims to develop new implements for archaeological research in prehistory and protohistory within the field of 2D digital imaging and 3D graphics, mainly, to produce automatic systems of recognition and classification of graphic data, such as pottery figurative decoration, through the use of computer vision and pattern recognition techniques and to develop virtual models of prehistoric sites and items with a high degree of accuracy following the data obtained during excavation and study, through application of laser scanner and 3D modeling techniques. A cognitive process based on a peer-to-peer exchange of knowledge between experts of computer science and prehistory working side by side. The cooperative experience of the Archeomatica Project, which represents (through its scientific production) the most recent trends in digital archaeology and the modern politics of conservation of archaeological heritage, has also aimed to define a common multidisciplinary language to improve the quality of the message of this new discipline to the outside world. In these first years of research activity the Archeomatica Project has produced significant results in archaeological 3D modeling and for 3D digital restoration, in order to improve the cognitive capacities of the archaeologists.
Archaeological 3D Modeling
Archaeological 3D modeling is basically the recreation of landscapes, architecture, and objects by digital means based upon the current state of the salvaged monuments integrated with the data coming from historical and archaeological researches using software for developing 3D models , without the application of reverse engineering methodology.
It is probably the most popular computer-based technique applied to cultural heritage as it represents the core of the “serious games” used in many multimedia projects . The archaeological 3D modeling is not just a simple cognitive tool to reproduce virtually aspects of the past, like objects of everyday life , to improve the knowledge and the comprehension. It is also, above all, a methodology of recording all the archaeological data in a much more complete way than the traditional photography and drawing and it is also an instrument of interpretation for the researchers who are involved in the theoretical reconstruction of the past itself. From this point of view, it is a kind of virtual benchmark of the archaeologists’ theories where the hypothesis is tested and corrected in order to produce a truthful image of something buried by time. A kind of “solid modeling to illustrate the monument” becoming “solid modeling to analyze the monument” . For this reason, the privileged application field for this technique is the prehistoric archaeological research, where, the scarcity of iconographical sources and the poor state of conservation of the findings, makes extremely complex both the process of decoding the information and of transmitting the knowledge to the public.
The researchers of the Archeomatica Project have chosen Blender  as a work tool, an open source cross-platform software for modeling, rendering, animation, post-production, creation, and playback of interactive 3D contents, extremely versatile, functional, and constantly open to implementations based on the research of its application in various fields. Where it was necessary for particular issues, image-based 3D modeling techniques, which consist in the elaboration of a 3D model from a set of high quality digital photos, have also been used [37,38].
The study cases chosen for testing the archaeological 3D modeling are the site of Haghia Triada (Crete, Greece) and Polizzello Mountain (Sicily, Italy), two pre-protohistoric archaeological complexes, which have been the subject of research of the archaeologists from the University of Catania for a long time, and which represent the full cultural evolution of Crete and Sicily between the second and first millennium BC. The decision was also supported by the small number of applications of 3D computer graphics on the Cretan and Sicilian archeology [39-41], a fact that greatly limits the interpretation study of evidences.
Haghia Triada, Crete
The site of Haghia Triada , in the Mesara plain in Crete (Figure 1.1), is one of the main sites of the Minoan civilization, constantly under study by the Centre for Cretan Archaeology of the University of Catania, under the permission of the Italian Archaeological School at Athens. The settlement of Haghia Triada has developed seamlessly over nearly two millennia, from the fourth to the second millennium BC, between the Early Bronze Age and the Early Iron Age. The flourishing of the site coincides with the Neopalatial period (from the seventeenth to the first half of the fifteenth century BC) and the Palatial Final period (from the second half of the fifteenth to the thirteenth century BC), that in terms of Minoan chronology correspond to Middle Minoan III, Late Minoan IB and Late Minoan IB, Late Minoan IIIB [43, 44].
During the Neopalatial period was built the so-called Royal Villa, a monumental L-shaped complex, including districts and stately buildings, but also vast areas of warehouses, administrative offices, which represented the symbols of territorial power, probably under the control of Knossos, which at this time had acquired a leading role in central Crete. North of the Villa, a small village was located, perhaps demonstrating the special nature and specific function of “administrative” capital of the site. Set between the Villa complex and the village, an open area was enriched by the presence of a stoa and a propylon, which has the function of mediation space from the noble to the popular quarter. At the end of Late Minoan IB (1450-1430 BC) a serious seismic episode destroyed the Villa and the village, leading to a period of relative neglect in the area until the end of the fifteenth century BC, coinciding with a major political and cultural event in the history of Crete: the occupation of the palace of Knossos, the traditional power center island, by people coming from Mycenaean Greece, which extended its control over the west central part of the island, constituting a true unitary state of Mycenaean type [45,46]. During the Palatial Final period, the Mycenaean phase of Haghia Triada started, a process of architectural uprising aimed to create a unified and comprehensive urban planning, providing, in the Villa, at least five public buildings and a series of constructions with political and religious functions, as the Megaron, the Shrine, and the Stoa. In the village was instead created the commercial and administrative center dominated by large stoa and a series of large buildings not only with residential functions, as the so-called House of Razed Rooms (Casa delle Camere Decapitate), dated to Late Minoan IIIA2 and interpreted as a warehouse for the storage of grain. In fact, besides only small buildings that were short-lived, and the monumental complex of the so-called VAP House (Casa dei Vani Aggiunti Progressivamente), dating from several stages in the Late Minoan IIIA2-IIIB, which can be identified with the elite residence that had control of the site, Haghia Triada is characterized as a singular houseless town. In the new system of Mycenaean power, the site of Haghia Triada, indicated in Linear B texts with the name of pa-i-to (Phaistos) must have been an important administrative center, a sort of district capital or a second order center, probably controlled by a group in direct contact with the elites of Mycenaean Knossos and aimed to the exploitation of resources of the surrounding area [45,47]. The intense construction activity that characterized the site during about four centuries, marked by duplication, destruction and reconstruction, transformation, and reintegration, becomes the main problem for the process of interpreting the evidence and its spatial and cultural contextualization. The traditional graphic and photographic documentation of the excavation, which in many excavations is dating back to early 1900, in some cases may be insufficient to fully decode both the diachronic and synchronic architectural issues. From this point of view, the Haghia Triada site is an ideal benchmark for the application of 3D Modeling technologies and a perfect test for the real potential that this tool had to offer in the process of historical reconstruction.
Diachronical plan of Haghia Triada.
Haghia Triada open area: (a) plan of the Propylon; (b) the Propylon in the current preservation state, from South; (c) the Stoa in the current preservation state, view from west.
Three monuments have been selected; these are considered the most problematic ones, both for the difficulty of interpretation and the architectural complexity. In a second phase of the study the case of the open area with the Propylon and the Stoa has been the focus of attention. It acts as a connecting element between the Villa and has been inhabited as early Neopalatial, and the House of Razed Rooms and VAP House, which was partially lived during the Palatial Final period. The decision to build the 3D models of these buildings, spatially adjacent but temporally successive, is part of the most ambitious project to create a 3D model of multi-plan site that can overcome the current phase plan , setting as the most advanced, modern, and expendable method of dissemination of the knowledge. In carrying out the work, two recurring problems were represented by the absence of a virtual model of the Haghia Triada ground: in which to locate the models, and the definition of light sources inside and outside of rebuilt buildings. The realization of the models was performed at different times and by different operators that followed, however, the same guidelines. In the initial phase of the project it was chosen to set the individual models in a virtual abstract ground model, waiting to start working with the project leaders of Crete Digital Satellite Remote Sensing Laboratory of Geophysical and Archaeo-environment of the Institute for Mediterranean Studies related to the Foundation of Research and Technology, Hellas (FORTH) , which already produced the Digital Terrain Model of the territory of Crete . This will provide the location in scale of individual reconstructed buildings in the virtual version of the hill of Haghia Triada. As for the lighting following prior experiences [39,51,52], it was chosen to replicate the natural light of a summer morning for outdoor models, whereas for interior without windows a virtual source of artificial light, like the flame of an oil lamp, a candle, or a torch, has been introduced, developing the model with the help of Radiance software .