During the recent years, especially after the beginning of the 21st century, we have witnessed a significant increase in the data collected by archaeological research concerning the pottery of the Byzantine era from a multitude of sites in the Mediterranean and specifically the region of present-day Greece. After the first decades of the 20th century, when the first major studies were published with an archaeological approach to this material, concerned with the classification of the main categories of Byzantine pottery, the more systematic work done in this field of material culture of Byzantium began in the 1980s onwards, and today this field of study is flourishing in Greece and the rest of the world. The accumulation of a multitude of data from many parts of the Mediterranean derives from the numerous related publications concerning primary source material that came into light either during systematic and rescue excavations, or in surface surveys.
 On middle-Byzantine glazed pottery, the categorization of which preceded that of the early Byzantine, see D. Talbot Rice, Byzantine Glazed Pottery, London 1930, and the more recent and more detailed work of Charles Morgan II; C. H. Morgan, II The Byzantine Pottery, Corinth vol. XI, Cambridge, Massachusetts 1942, which systematized the relevant categorization. On the red-slipped pottery and the amphorae of the early Byzantine period, see indicatively J. W. Hayes, Late Roman Pottery, London 1972, and J. A. Riley, “The Pottery from the First Session of Excavation in the Caesarea Hippodrome”, Bulletin of the American Schools of Oriental Research 218 (1975), 25-63; J. A. Riley, “The Carthage System of Quantification of Pottery”, in: J. H. Humphrey (ed.), Excavations at Carthage 1975 Conducted by the University of Michigan, v. 1, Tunisia 1976, 125-156; J. A. Riley, “The Coarse Pottery from Berenice”, in: J. A. Lloyd (ed.), Excavations at Sidi Khrebish Benghazi (Berenice), v. 2, Libya Antiqua suppl. V.2, Tripoli 1979, 91-467.
 K. Dark, Byzantine Pottery, Gloucestershire, Charleston 2001,7-8, 28-29; Α. G. Yangaki, “Η κεραμική στην Κρήτη τη μεσαιωνική και νeεότερη εποχή: Σύντομη επισκόπηση της έρευνας” (Pottery in Crete during the Medieval and Modern times: A brief overview of the research), in: Α. Yangaki, O. Gratziou (eds.), Πανεπιστήμιο Κρήτης. Φιλοσοφική Σχολή – Τμήμα Ιστορίας και Αρχαιολογίας. Εκπαιδευτική Συλλογή Μεσαιωνικής και Νεότερης Κεραμικής. Κατάλογος, Rethymnon 2012, 23-25; P. Petridis, Πρωτοβυζαντινή κεραμική του ελλαδικού χώρου, (Early Byzantine pottery from Greece), Athens 2013, 19-25; P. Petridis, “Η ιστορία της έρευνας της βυζαντινής κεραμικής και τα νέα δεδομένα στην επιστήμη της κεραμολογίας” (The history of research on Byzantine pottery and the new data in the field of ceramology), in: Τριακοστό Τέταρτο Συμπόσιο Βυζαντινής και Μεταβυζαντινής Αρχαιολογίας και Τέχνης. Πρόγραμμα και Περιλήψεις Εισηγήσεων και Ανακοινώσεων. Αθήνα, 9, 10 και 11 Μαΐου 2014. Βυζαντινό και Χριστιανικό Μουσείο, Βασ. Σοφίας 22, Αθήνα, Athens 2014, 110-111.
Characteristics of the digital application and research limitations
First of all, some clarifications should be made as to the method used in the indexing, the data displayed on the maps and the contents of the database that supports them, in order to clarify the type of information that, based on the available published data, it was possible to deal with, always keeping in mind the maximum usefulness of the result.
Case studies for data mapping. The Peloponnese and Crete
The area of the Peloponnese was chosen because of the particular and long-term attention given to its history by the research programme of the Institute of Historical Research “Historical Geography of the Greek Region” , and because of the relevant pottery material published, which offers a representative sample from mainland Greece, and particularly from many sites and for the entire time frame in question (4th-15th centuries), compared to the data from other areas of wider Greece.
Additionally, the insular area of Crete has been added, as it constitutes another region of the Aegean for which a plethora of data on Roman, Byzantine and Venetian pottery has been collected during the last decades. Our interest focused on the indexing of the pottery found on the island from the 4th century to the 16th, in order to have a comparable specimen to the data from the Peloponnese. Concerning the data from Crete, as the volume of the relevant information deriving from these two geographical regions is large, the data presented here was drawn from the coastal areas of the island and just some locations in the island’s mainland. The aim was to highlight the various categories of ceramics located in these areas in the course of the centuries under investigation. Much data from the city of Gortyn were included in the current project. Through the maps that emerged from the two case studies, the data on the ceramics found in these areas of Greece can be compared and contrasted, revealing common networks and cases of trade contacts between them.
On this research project and its various activities, see: http://www.eie.gr/nhrf/institutes/ibr/programmes/histgeo-gr.html (access 25/08/2014).
 The relevant literature is numerous, as can be seen by the data in the fields of the database. For further information, A. G. Yangaki, “Παρατηρήσεις στη μεθοδολογία και στη μελέτη της κεραμικής του 11ου-12ου αι., προοπτικές της έρευνας και επιβοηθητικά εργαλεία: Η συμβολή της χαρτογράφησης και της ανάλυσης δικτύων”, Byzantina Symmeikta 25 (2015), 187-188; A. G. Yangaki, “Pottery of the Byzantine period, trade networks, mapping, network analysis: A case study”, Journal of Archaeological Science. Reports 21 (2018), 1104-1106.
For the indexing of the published data, that existing were downloaded from the application that had been created in the older project CONVEX GRIDS into a specially designed database in HEURIST, where the corresponding fields were maintained. To this core were added the additional data, derived from the systematic indexing of Greek and foreign bibliography regarding the ceramics from the Peloponnese and Crete. These were downloaded to a program-specific spatial data database (mySQL), from which a digital, interactive, geographic atlas emerged through the use of a geographic information system application. A worksheet was started in Microsoft Excel, with fields conveniently adapted to the needs of the project: and the relevant data entered. The worksheet was uploaded into the geographical space database (specially designed for the project) running MySQL, which produced a digital interactive geographical atlas, through a GIS application, ArcGIS.
 For further details on other works, where relevant applications are used, see Yangaki, “Παρατηρήσεις στη μεθοδολογία”, 191-192 notes 120-123.
During the data collection process, and when a large part was ready for processing, a high degree of variability in the way it was presented in the various publications became obvious, and it was deemed necessary to make certain compromises concerning the digital presentation of the material to achieve the best possible depiction. In short, we faced certain methodological problems which were reflected in the database content.
First, with certain sites, such as Ancient Corinth or Argos, the data relative to Byzantine pottery information is extremely wide. When it derives from many different excavated locations in the wider area of the urban space, we have adopted the use of one common geographical location mark for the entire area in order to make it easier for the user. In this way, the map is more readable, as otherwise a veritable forest of markers would be required for the tens of positions for the same urban spot. In order, however, to be specific about the position each material came from, more information on the excavation and its location was given in the Remarks field. A similar practice was used for the individual positions across a wider surface survey: the broader particular area has been noted, with separate references on each location in the Remarks.
Furthermore, the fragments or vessels were noted by the basic form to which they belong, followed by their typological classification, based on specific types recognized (see below in text). According to the basic vessel forms, as noted in the publications, the material indexed was then presented in groups of larger categories of pottery (Tablewares, Cooking Wares, Transport and Storage Vessels, Lamps, Other), which can be further searched in combination with particular types of pottery vessels.
Although in recent years most scholars have adopted specific classification systems to refer to the most known and widespread types of pottery, many times, and usually in the much older publications on pottery from the Peloponnese and Crete, the specimens presented are not clearly assigned to any category of pottery. Taking into consideration all the above, and to achieve a consistent depiction of the data, it was deemed best to use the typological classifications most generally employed for the entry of the basic data. This comprises the use of names established in Greek and other languages for the description of other categories, which are not included in the aforementioned classifications. Given that, as noted by other researchers, it is quite common to find publications where a vessel shape is ascribed to the wider type of a known typological classification, without stating the subcategory to which it belongs, and furthermore, as we often lack the ability to extract the relevant information from the limited information printed, we have chosen to give the references in the general classification. Wherever it was possible to extract with safety specific relevant information, more details on the typology are given in the field Remarks. Thus, we can achieve a larger homogeneity in the used terminology.
 For the fine-quality, red-slipped pottery of the early Byzantine period we have adopted the typological classification of J. W. Hayes (Late Roman Pottery). For the glazed pottery of the middle and late Byzantine periods we follow the classification by Ch. Morgan, II (The Byzantine Pottery) and for its rendering in Greek, the one presented in D. Papanikola-Bakirtzi (ed.), Βυζαντινά εφυαλωμένα κεραμικά. Η τέχνη των εγχαράκτων, (Byzantine glazed ceramics. The art of sgraffito), Athens 1999. For the rendering in Greek of the terminology used for the imported from Italy categories of glazed pottery, see A. G. Yangaki, Εφυαλωμένη κεραμική από τη θέση «Άγιοι Θεόδωροι» στην Ακροναυπλία (11ος-17ος αι.) (Glazed pottery from the “Hagioi Theodoroi” site in Akronauplia (11th-17th c.)είναι ο επίσημος τίτλος), Athens 2012. For the typology of the amphorae we have used for the early and middle Byzantine periods the classifications by J. A. Riley (“The Pottery from the First Session”, 25-63; “The Carthage System of Quantification of Pottery”, 125-156; “The Coarse Pottery from Berenice”, 91-467) and N. Günsenin (N. Günsenin, “Recherches sur les amphores byzantines dans les musées turcs”, in: V. Déroche, J.-M. Spieser (eds.), Recherches sur la céramique byzantine [Bulletin de Correspondance Hellénique suppl. XVIII], Athens, Paris 1989, 267-276) and of J. W. Hayes (J. W. Hayes, Excavations at Saraçhane in Istanbul, v. 2, The Pottery, Princeton 1992, 61-78), respectively.
 The comments by S. Demesticha are indicative of the recognition of individual variants of the late-Roman amphora 1 (S. Demesticha, “Amphora Typologies, Distribution, and Trade Patterns: The Case of the Cypriot LR1 Amphorae”, in: M. L. Lawall, J. Lund (ed.), The Transport Amphorae and Trade of Cyprus [Gösta Enbom Monographs 3], Aarhus 2013, 171-175).
This project also focuses, as mentioned earlier, on elucidating the trade contacts of places in the Peloponnese and Crete with other areas. These can be studied by considering the imported pottery of each site. Besides, it should be noted that the relevant published data favors the presentation of imported products at a site, mainly good-quality pottery, tablewares, amphorae and lamps. Data on other categories of pottery, which could equally be traded objects, such as cooking wares, are greatly limited. For this reason, only data on the aforementioned types of imported pottery (fine-quality tablewares, amphorae, lamps) has been selected and given, and only in a few cases on the cooking wares or the very characteristic categories of plain wars, where information in the bibliography confidently assigned them to specific centers of outside production.
Categories thought to be local products from Peloponnesian sites where they are found, or categories for which the researchers do not comment on as to whether they are imported or local specimens, have all been omitted. Concerning clay lamps, in particular, it is common for them to be manufactured beyond their main production zone, i.e. in various regional lamp workshops that follow a specific, widely spread, morphology, such as the lamps belonging to the so-called ‘North-African’ type. Moreover, in most publications it is not clear whether the examples are recognized as imported or only as local products. With all this in mind, only the specimens for which there is an expressed opinion that they are imported have been entered.
Concerning the content, it should be here observed that in most publications either only one pot specimen from a specific position or an excavation site is presented, usually with an emphasis on its diagnostic examples (e.g. the fine-quality, red-slipped pottery of the early Byzantine period, or the glazed pottery of the middle and late Byzantine periods or the amphorae), or there is no clear excavation data for the dating of the pottery, which is rather placed in time according to comparative material from other sites. Furthermore, in a preliminary presentation of a material, no clear data on the quantity for each category of pottery per contexts may exist. On this latter point, the data is also expressed often inadequately: either the quantity is never given, or it is given in a relative way (for example, in addition to the most characteristic sherds presented in detail, there is a mere mention, in relative numbers, to others in the same group). There is no complete quantitative examination of the material, nor a clear indication as to whether any given quantity truly represents the entire group; all this means one must approach these sort of quantitative remarks with caution. In very few cases do we have detailed quantitative data that can be used safely. As a result, the existence of a pottery category in different places is first marked with a simple sign in all cases on the map. It is then further marked as A, B or C, to inform the user about whether (a) there is absolutely no quantitative data in the relevant bibliography, or (b) the data is not particularly clear, or (c) it is detailed. Therefore, given the particular limits imposed by the research data, the user must bear in mind the possibility that some of the depicted information may involve but isolated specimens, and should not be interpreted as indications of organized commercial activity, but merely as indicators of the diffusion of one category of pottery in the Peloponnese and in Crete. Related hazards have also been remarked upon in the past for data depicted on non-digital maps. The user must consult the specific publications, in order to certify the type of quantitative information given.
As for the dating, we reproduce the one given in each original publication. However, in cases where there are more recent publications that revise the dating, the respective chronological indication has been adjusted to the latest ones (such cases can be found in material from Ancient Corinth and sites of Crete). Relevant comments and bibliography are given in the field titled Remarks. Furthermore, for the cases where the proposed dating in the publication leads to doubts, when likened with the general data existing for the dating of specific types of pottery, we have used the question mark (?) to note the fact.
 For the use of map symbols which offer quantitative data on the pottery of the early Byzantine period with great clarity, a recent example comes from surface research in Cyprus (K. Winther-Jacobsen, “Supply Mechanisms at Non-agricultural Production Sites. Economic Modelling in Late Roman Cyprus”, in: M. L. Lawall, J. Lund (eds.), The Transport Amphorae and Trade of Cyprus [Gösta Enbom Monographs 3], Aarhus 2013, 203-207 with image 1). In this case, however, it is a research in primary pottery material.
 On the lack of systematical reference to quantitative data and its effects, see also J. Dimopoulos, “Byzantine Graffito Wares excavated in Sparta (12th – 13th Centuries)”, in: B. Böhlendorf-Arslan, A. O. Uysal, J. Witte-Orr (eds.), Çanak. Late Antique and Medieval Pottery and Tiles in Mediterranean Archaeological Contexts (BYZAS 7), Istanbul 2007, 345; I. Dimopoulos, “Trade of Byzantine Red Wares, end of the 11th-13th centuries”, in: M. Mundell Mango (ed.), Byzantine Trade 4th-12th Centuries. The Archaeology of Local, Regional and International Exchange. Papers of the Thirty-eighth Spring Symposium of Byzantine Studies, St John’s College, University of Oxford, March 2004 (Society for the Promotion of Byzantine Studies Publications 14), Farnham, Burlington 2009, 185; V. François, “Représenter le commerce de la poterie à Byzance”, in: É. Malamut, M. Ouerfelli (eds.), Les échanges en Méditerranée médiévale. Marqueurs, réseaux, circulations; Contacts, Aix-en-Provence 2012, 36. See also Yangaki, Glazed pottery from the “Hagioi Theodoroi”, 112.
On a second level, concerning the possibility of the depiction of trade “networks”, we must remark at this point that the data presented are not to be characterized by the narrow term of ‘trade network’. On the contrary, when approaching the issue of commercial contacts between different sites based on archaeological finds, the term is used in a more general sense, often as a synonym for communication, of the existence of ‘nodes’ and the ‘links’ between places – positions linked by having pottery categories in common. A further assessment of the specimen, combined with written sources, may of course lead to conclusions that do highlight detailed commercial networks
For the presentation and recognition of the ‘networks’, as defined earlier, we obviously need two nodes, one corresponding to the place of discovery, and one corresponding to the place of origin. The archaeological indications, however, for locating the production workshops remain very small in number. Even smaller is the data concerning the secure recognition of their products in their consumption places. Even so, such pottery categories are considered, in most cases, as indeed representing pottery imports into their find locations in the Peloponnese and Crete, given the opinions stated about their origin. In certain cases, these have been confirmed, based on archaeological or archaeometric data. Therefore, the shaping of the network is made according to proximity, i.e. a wider zone is presented as the place of production for specific categories of pottery, when considered or proven from research to be the area in which the center(s) of production were sited. For example, the categories of protomaiolica or archaic maiolica has been confirmed to have been produced in sites in southern and northern-central Italy, respectively, without, however, it being possible to attribute specimens from the Peloponnese to specific centers in Italy. Therefore, these two wider zones were chosen to define the general area of origin of the specimens, and the respective geographical location has been so conventionally defined.
Moreover, the wide span of the mid-Byzantine glazed pottery group includes many categories; this has been in the spotlight of research. For example, it has been argued that in parallel to an obviously well-organized center supplying both neighboring and distant markets with its products recently located in the area near Chalkis, secondary centers of production existed. The diffusion of their products to other locations can still not be proven with certainty in most cases. Based on this information, one spot has been conventionally chosen for the origin of this pottery, placed in the area of the Aegean, near Chalkis, which is considered to have been a very important center of production. Again, the early Byzantine red-slipped pottery of North Africa was produced in a variety of centers of this region, many of which are known to us, but we cannot associate the imports found in the Peloponnese with specific centers. Thus, we have marked the entire region of North Africa as their place of origin. On this basic approach, the approach of modern research in the effort to reinstate the commercial ties between positions in the Mediterranean is founded, now depicted with the relevant data on a map. There are also pottery categories for which research does not have any information on the place(s) of production, despite the fact that they are considered to be generally imported into the areas where they are found. In these cases, the material was indexed without being associated with a specific center of production, in the hope that future research will give us more data on its origin.
 For further details on all the above, see Yangaki, “Παρατηρήσεις στη μεθοδολογία”, 188-199.
 S. Y. Waksman, N. D. Kontogiannis, S. S. Skartsis, G. Vaxevanis, “The Main “Middle Byzantine Production” and Pottery Manufacture in Thebes and Chalcis”, The Annual of the British School at Athens 109 (2014) 379-422.
 Typicallya see G. D. R. Sanders, “Παραγωγή των εργαστηρίων της Κορίνθου” (The production of the Corinth workshops), in: Papanikola-Bakirtzi, Βυζαντινά εφυαλωμένα κεραμικά, 162; G. D. R. Sanders, “Recent Developments in the Chronology of Byzantine Corinth” in: C. K. Williams, II, N. Bookidis (eds.), Corinth, The Centenary 1896-1996. Corinth vol. XX, The American School of Classical Studies at Athens 2003, 388-395; O. Vassi, “An Unglazed Ware Pottery Workshop in Twelfth-Century Lakonia”, BSA 88 (1993) 292; D. Papanikola-Bakirtzi, “Εργαστήρια εφυαλωμένης κεραμικής στο βυζαντινό κόσμο” (Glazed pottery workshops in the Byzantine world), in: Ch. Bakirtzis (ed.), 7ο Διεθνές Συνέδριο Μεσαιωνικής Κεραμικής της Μεσογείου, Θεσσαλονίκη, 11-16 Οκτωβρίου 1999, Πρακτικά, Athens 2003, 53; Α. Oikonomou-Laniado, “Βυζαντινή κεραμική από το Άργος (12ος-13ος αιώνας)”, in: D. Zafeiropoulou (ed.), Α΄ αρχαιολογική σύνοδος Νότιας και Δυτικής Ελλάδος, ΣΤ΄ Εφορεία Προϊστορικών και Κλασικών Αρχαιοτήτων, 6η Εφορεία Βυζαντινών Αρχαιοτήτων, Πρακτικά, Πάτρα 9-12 Ιουνίου 1996, Athens 2006, 346; Dimopoulos, “Byzantine Graffito Wares”, 336, 339.