A critical review of the hypothesis of a medieval origin for portolan charts i Roelof Nicolai A critical review of the hypothesis of a medieval origin for portolan charts Keywords: portolan, chart, medieval, geodesy, cartography, cartometric analysis, history, science ISBN/EAN: 978-90-76851-33-4 NUR-code: 930 Uitgeverij Educatieve Media, Houten. E-mail: [email protected] Vormgeving en drukwerkrealisatie: Atalanta, Houten Cover design: Sander Nicolai The cover shows part of the Carte Pisane, Bibliothèque nationale de France, Cartes et Plans, Ge B 1118. Copyright © by Roelof Nicolai All rights reserved. No part of the material protected by this copyright notice may be repro- duced or utilised in any form or by any means, electronic or mechanical, including photocopy- ing, recording or by information storage and retrieval system, without the prior permission of the author. ii A critical review of the hypothesis of a medieval origin for portolan charts Een kritische beschouwing van de hypothese van een middeleeuwse oorsprong voor portolaankaarten (met een samenvatting in het Nederlands) Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof.dr. G.J. van der Zwaan, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op maandag 3 maart 2014 des middags te 2.30 uur door Roelof Nicolai geboren op 20 november 1953 te Achtkarspelen iii Promotor: Prof. dr. J. P. Hogendijk Co-promotoren: Dr. S. A. Wepster Dr. P. C. J. van der Krogt iv He had bought a large map representing the sea, Without the least vestige of land: And the crew were much pleased when they found it to be A map they could all understand. “What’s the good of Mercator’s North Poles and Equators, Tropics, Zones and Meridian Lines?” So the Bellman would cry: and the crew would reply “They are merely conventional signs!” Lewis Carroll, “The Hunting of the Snark”, 1876 v vi TABLE OF CONTENTS Preface ....................................................................................................................................................xiii Summary ................................................................................................................................................xvii Samenvatting ..........................................................................................................................................xxi Introduction .............................................................................................................................................1 Research question ...................................................................................................................................3 Scope ..........................................................................................................................................................4 Structure of the thesis .............................................................................................................................5 1 The historical context of the emergence of portolan charts ............................. 11 1.1 The medieval Mediterranean – relevant historical aspects ...................................11 1.1.1 The awakening of Europe ..........................................................................12 1.1.2 The Italian maritime republics and Aragon .............................................14 2 Key characteristics of portolan charts ................................................................25 2.1 Distinguishing cartographic characteristics .............................................................25 2.2 Disputed, unclear and unsatisfactorily explained aspects of portolan charts .....32 2.2.1 Exaggeration of coastal features ...............................................................33 2.2.2 A contradiction of Tobler’s First Law of Geography ............................36 2.2.3 First appearance ...........................................................................................38 2.2.4 The lack of any development path ...........................................................40 2.2.5 Scale variations .............................................................................................44 2.2.6 The rotation of the map image .................................................................45 2.2.7 Chart accuracy and map projection ..........................................................46 2.2.8 Stimulus for chart development.................................................................47 2.2.9 Conservatism ................................................................................................51 3 Existing hypotheses on the origin and construction method of portolan charts..55 3.1 Scholarly views on the origins debate .......................................................................55 3.2 Ideas on antique origins ..............................................................................................57 3.2.1 Neolithic origins ...........................................................................................57 3.2.2 Egyptians, Phoenicians and Marinus of Tyre ..........................................58 3.2.3 Roman centuriation .....................................................................................59 3.2.4 Unspecified antiquity ...................................................................................60 3.2.5 Ramon Pujades’s views................................................................................61 3.3 Hypotheses on medieval origins ................................................................................62 3.3.1 Relationship with portolans; Byzantium ..................................................62 3.3.2 The Holy Roman Emperor Frederick II of Hohenstaufen ..................63 3.3.3 Leonardo of Pisa (Fibonacci) ....................................................................64 3.3.4 Benedetto Zaccaria ......................................................................................64 3.3.5 Aragon ...........................................................................................................65 vii 3.3.6 Unspecified multiple origins .......................................................................65 3.3.7 Other views ...................................................................................................65 3.4 Hypotheses on portolan chart construction ............................................................67 3.4.1 Concatenated coastal sketch maps ............................................................67 3.4.2 Geodetic control network from marine observations ............................67 3.4.3 Geodetic control network based on astronomic positions ...................69 3.5 Plane charts and plane charting .................................................................................70 3.5.1 Other authors’ views ...................................................................................70 3.5.2 Plane charting – a simple example ............................................................73 3.5.3 Analysis and four more arbitrary routes ...................................................77 3.5.4 Conclusions on plane charting ...................................................................79 3.5.5 Square grid – earth curvature ignored?.....................................................80 3.6 The rotation angle ........................................................................................................81 3.7 Methodological considerations ..................................................................................86 4 Physical conditions of the Mediterranean Sea; medieval ships ..........................91 4.1 Outline of this chapter ................................................................................................91 4.2 The natural conditions in the Mediterranean ..........................................................91 4.2.1 Surface currents ............................................................................................92 4.2.2 Wind in the Mediterranean .........................................................................95 4.2.3 Coastal topography and hydrography .................................................... 102 4.2.4 Implications for portolan chart origins ................................................. 102 4.3 Medieval ships............................................................................................................ 104 4.3.1 Round ships ............................................................................................... 104 4.3.2 The lateen rig ............................................................................................. 107 4.3.3 Galleys ........................................................................................................ 110 4.3.4 Implications for portolan charts origins ................................................ 115 5 Navigational practices in the twelfth and thirteenth centuries ......................... 117 5.1 Introduction and outline of the chapter ............................................................... 117 5.2 Navigational tools: chart & dividers, needle & star ............................................. 119 5.3 The Toleta de Marteloio ................................................................................................ 121 5.4 The mathematical seaman .......................................................................................