the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 May 2026
Classical Antiquity Origin of Spatial Data Underlying Portolan Charts: How Pietro Vesconte Might Have Assembled the Carta Riccardiana Utilising Maps in Marinus of Tyre’s projection
Abstract. The remarkably accurate representation of coastlines on late mediaeval portolan charts has garnered significant scholarly interest in uncovering the origin of their spatial data, with the prevailing hypothesis suggesting that they are authentic products of their time, created by synthesising numerous shipborne bearing and distance measurements. The pursuit of those answers also prompted the establishment and advancement of a cartometric approach, through which they can be attained with quantitative accuracy. This study is based on cartometric analyses and historical evidence, providing a comprehensive examination of the anonymous Carta Riccardiana portolan chart, presumably created by Pietro Vesconte between 1300 and 1325. It posits a paradigm shift regarding the late mediaeval origin hypothesis, tangibly indicating that the conventional geometry of portolan charts was likely developed by late mediaeval copyist-cartographers who utilised regional maps from classical antiquity, originally made in the projection of Marinus of Tyre calibrated to their mid-latitudes as inputs, which they partially scaled and gradually tilted, using a map in Ptolemy’s first projection as a reference model. Concurrently, the article provides a historical overview of the most significant cartometric studies in the field, critically analysing their unique systemic parameters that have influenced various hypotheses regarding the origin of portolan charts—specifically, the systemically induced similarity with the modern map in the Mercator projection, which is, in the case of the Carta Riccardiana, at least, a misleading notion.
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Status: final response (author comments only)
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RC1: 'Comment on hgss-2026-2', Anonymous Referee #1, 27 May 2026
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AC1: 'Reply on RC1', Tome Marelić, 07 Jun 2026
I express my sincere gratitude to the reviewer for acknowledging the quality of this article. The recommendation to provide additional clarification regarding Pietro Vesconte in the text is entirely valid, and I will certainly endeavour to include it in the revised version.
I will compose the official response to this review report in my final reply following the open discussion, which will occur after June 8 in this instance.
Citation: https://doi.org/10.5194/hgss-2026-2-AC1
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AC1: 'Reply on RC1', Tome Marelić, 07 Jun 2026
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RC2: 'Peer review report #2 of hgss-2026-2', Roel Nicolai, 27 May 2026
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AC2: 'Reply on RC2', Tome Marelić, 07 Jun 2026
I greatly appreciate the reviewer's approach regarding the topic and evaluation of the subject matter. Due to the review report of this article being exceptionally comprehensive and meticulous, I have been engaged in formulating the response throughout this period.
I have prepared the document detailing my responses to each reviewer's critique, encompassing all six general comments from (a) to (f) and all 24 specific comments in the table. I must still examine the linguistic components and specifics, after which I will upload it as my final response subsequent to the open discussion a few days post-June 8.
At present, I can only state that I have addressed each criticism, defending the current hypotheses while presenting new arguments and evidence. The comments have proven beneficial, prompting me to develop revisions that will enhance the article's quality and further corroborate the hypotheses.
Citation: https://doi.org/10.5194/hgss-2026-2-AC2 -
AC3: 'Reply on RC2 containing detailed response document in PDF with table and figures', Tome Marelić, 07 Jun 2026
A detailed response to this review report that I promised to deliver in the prvious comment is now complete, and its PDF document is attached to this comment.
Given that it originates from a colleague who has dedicated the past two decades to investigating the origins of portolan charts and whose doctoral dissertation served as my most influential model when I first began researching this subject, it is unsurprising that this is one of the most comprehensive and lengthy peer review reports I have received regarding my research output to date. For a variety of reasons, my response to the review report is particularly extensive.
The reviewer pointed out specific flaws in the initial draft of the scientific paper, including the absence of certain arguments or details or inadequate explanations. As a result, I tried to give the reviewer and the journal's editors as much detail as I could about my theories and viewpoints.
Furthermore, since the HGSS journal employs a public peer review model, all of these documents inevitably become (and continue to be) attached to the article as a thread of metadata. Consequently, I have endeavoured to provide a more comprehensive and transparent explanation to a broader audience.
Lastly, I purposefully wrote longer answers to some of the reviewer's criticisms and accompanied them with newly made tables and newly made figures. I plan to incorporate those elements into the revised version because they provide even more convincing evidence for the hypothesis that the spatial data underlying portolan charts originated in classical antiquity.
Tome Marelić
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AC2: 'Reply on RC2', Tome Marelić, 07 Jun 2026
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This article examines the previously little-known “Carta Riccardiana” in terms of its accuracy. Combining cartometric analyses with established historical data, this study offers the first clear and comprehensible explanation of how late medieval Italian copyists and cartographers may have compiled this composite data. This research provides a well-founded and detailed refutation of the hypothesis concerning medieval data sources for the creation of portolan charts, thus breaking new ground in scholarship. Maps from the late Middle Ages remain a relatively under-researched topic in the history of cartography to this day. The text is clearly organised, with well-structured chapters. The methodological approach has been explained. There are a sufficient number of illustrations, which are of good quality. The topic effectively bridges the history of cartography with modern cartography, and the article should definitely be published. The article fits very well in the journal, and the title accurately reflects the content of the text. The author possesses the necessary knowledge of history, geography and cartography to write on this topic. The peer reviewer notes only the following minor detail: The “Carta Riccardiana” is attributed to Pietro Vesconte in the article. But who was this man? A biography would certainly be of interest to readers. The methodological approach of modern cartography appears solid. The historical approach and information are fine, except for the missing biography. The English also seems to be fine. However, the peer reviewer is not a native speaker and therefore cannot provide a final assessment.