Simulating Sea Surfaces for Modeling Viking Age Seafaring in the Baltic Sea
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Simulating Sea Surfaces for Modeling Viking Age Seafaring in the Baltic Sea George Indruszewski' and C. M. Barton^ 'Viking Ship Museum Roskilde, Denmark ^School for Human Evolution and Social Change Arizona State University Tempe, AZ, USA [email protected] Abstract Inferences in nautical and maritime archaeology about sailing routes in the Viking Age in Northern Europe are based today almost entirely on historical information coupled with results gained from experimental archaeology. The authors propose here a third method, which combines computer simulation with the aforementioned information sources. These sources are used together with digital bathymétrie models (DBM's) of the Baltic seafloor, wind, current, and other real sailing parameters to create cost surfaces for modeling early medieval seafaring. Real sailing data obtained in the summer of 2004 with the Viking Age replica, Ottar, are used to model sea routes in the Baltic Sea. Both GlS-Esri and GRASS GIS are compared as modeling tools and used in least-cost path and anisotropic spread analyses to simulate sea routing in prehistoric land- and seascapes across which humans traveled more than a thousand years ago. The results of the study are evaluated in the context of experimental archaeology and modem sailing conditions in the Baltic Sea. 1 Introduction Maritime archaeology and, especially, historical research Blecingœg ond Meore ond Eowland ond Gotland dealing with Viking Age seafaring, have tried for a long time on bœcbord, ond Pas land hyraö to Sweon. Ond Weonodland wœs us ealne weg on steorbord od to decipher the reasons behind the choice of a specific sea Wislemudan. Seo Wisle is swyae mycel ea ond itinerary connecting medieval trading centers in the Baltic hio tolid Witland ond Weonodland: ond Paet realm. The problem is complex because explicit itineraries Witland bel imped to Estum; ond seo Wisle lid ut of from that period do not actually exist and the literates who Weonodlande ond lid in Estmere; ond se Estmere have laid them on the parchment for the posterity used their is huru fifteen mila brad. Panne cymed Ilfing epoch's writing style and conventions. This is the case, eastan in Estmere ofdaem mere, de Truso standed for example, with the early IS"" century King Valdemar's in stade, ond cumad ut samod in Estmere, Ilfing Itinerary from Utlängan (Sweden) to Reval (Estonia) where eastan of Estlande ond Wisle sudan ofWinodlande. the route follows the Swedish coastline in earnest (Varenius Ond Ponne benimd Wisle Ilfing hire naman, ond liged of Paem mere west ond nord on sae; for 1995:189-194). Adam of Bremen's late 11* century dy hit man haet Wisle muda.' (Alfred's Orosius ecclesiastic history, on the other hand, listed only the main Chorographia, 20) descriptive elements of a sea voyage: the departure point, the destination, and the time spent in reaching the destination (Adam of Bremen II, 22, in Schmeidler 1917:80). The English translation of the text (Bately in press) The situation becomes even more difficult when informs us that Wulfstan sailed for seven days and nights addressing the problem in the Viking Age period (8* to 11* from Haidaby, in the lower Schlei Fjord (in today's century AD), for which very few written sources are available Schleswig-Holstein, Germany) to Truso, near the Vistula for the interested scholar. One such source is the account of River mouth (identified archaeologically with Janowo Wulfstan, from the late 9"' century AD Orosian history of Pomorski, located ca. 4 km south of Elbl^ in Eastern King Alfred the Great, containing a short description of a Pomerania, Poland) (Figure 1 ). During the voyage, he had real sea voyage. on his starboard side Weonodland, that is the Land of the Wends in southern Baltic, to the port were the islands under Wulfstan sœde t>œt he gefore of Hœôum, Pœt he Danish overlordship (Langeland, LoUand, and Falster), weere on Truso on syfan dagum ond nihtum, t>cet followed by Bomholm, More, Blekinge, Öland, and Gotland Pcet scip wœs ealne weg yrnende under segle. (the latter belonging to the Svear). Weonodland him wœs on steorbord ond on bcecbord him wœs The text is important for several reasons. Its briefness, Langaland ond Lœland ond Falster ond Sconeg, composition, and informal content point altogether to a ond t>as land eall hyrad to Denemearcan. Ond description of a real sea voyage that happened sometime t>onne Burgenda land wœs us on bœcbord, ond in the second half of the 9* century AD, thus making the t>a habbad him sylfcyning. t>onne œfter Burgenda text one of the very few sailing narratives of the Viking Age lande wœron us t>as land Pa synd hatene œrest Baltic Sea that survived up to our times. George Indruszewski and C. M. Barton W ^^^^KÊ^M ^ .^^^^^^^^^^^^^^^^^^^H^Bi^l^H^^^^^^^^K.l^^^^^HKilBK' '.. ^jBi ^F 'ÜSffand s^^^^^^^^^Bb^ 1 f />^^ró fl vi W^^^^^^KÊÊÊ^KK; Moere ^p "••'.....•• ^^HHMRK' * bornholm Lan'gèia'nd ^ ^ ^ . , , ,. , , ,. • Falster • • • -^^^ smm^ .... f-pmnd '^9^m ^H ' '•- ^W ' ' ' . , mmsm^ •l^ÄTrusoft'""" ••••'••' ^ VVeonodtand (Elblag) Haldaby ««onod.and ":. ^^^ (Schleswig) -aü^L H Hamburg Î^H^HlHB A k ^ " 1 Figure 1. Grid locations (white "+") of wind and current data collected for the Baltic Sea for July 2004; historical place-names are in yellow (Haidaby, Weonodland, Weonodland, Trusco), other place names are white. Furthermore, its uniqueness lies not only in its narrative (1983:32-44). Relying upon iconographie evidence fi^om power of a sea voyage, but also in the fact that it is mentioning the Bauyeux Tapestry and other medieval historical sources, sea travel between two important, archaeologically- Crumlin-Pedersen pioneered a novel conceptual approach documented, trading centers from the Viking Age Baltic: to early Medieval Norse navigation that emphasized the Haidaby (Haithabu) and Truso (Janowo Pomorski). Last importance of depth sounding. He suggested that Wulfstan but not least, the text provides us with informational clues used sounding to follow a pre-selected bathymétrie line (he related to the way navigation was accomplished at that proposed using the -10 or-20 m depth lines) running along time. In the narrative, the author displays a geographical the southern Baltic coastline, from the mouth of the Schlei knowledge employing a maritime orientation system with to the mouth of the Vistula (1983: 42-43). In other words, the ship as the central point. That is, he does not orient Crumlin-Pedersen argued that the primary orientation the coastlines and islands in relation to each other, but in system for the Viking Age navigator was below the waterline relation to the sailing ship. This contrasts with Alfred's and not above it, and that coastal sailing was the main type Orosius orientation system(s) (Korhammer 1985:251-269), of navigation knowledge for that period. Besides the fact and is also unique among historical sources in general. that the author used iconographie and historical sources Paradoxically, but not unexpected, it is least ambiguous in reflecting a post-Viking Age reality, the proposed construct terms of cardinal directions. When Wulfstan said that the conflicts not only with the Wulfstan's textual information, islands under Danish suzerainty were on the port side, and but also with the character of his voyage. His sea voyage was that Weonodland was on starboard all the way until the routine sailing, which required neither sounding navigation Vistula mouth, it is clear that his ship sailed on a general nor coastal sailing, and this statement is supported not course from west to east. only by the historical text itself but also by the following arguments: 1. As a method of orientation at sea, sounding was 2 The Research Issue documented in Northern Europe later in the Middle Ages, although it was known since Herodotus' times Nevertheless, that is all the text explicitly indicates, and in the Mediterranean region. And when documented, the specific routing is left to more speculative hypotheses sounding is mentioned only in relation to landing or like the one envisioned by Crumlin-Pedersen in 1983 approaching a coastline. 476 Simulating Sea Surfaces for Modeling Viking Age Seafaring in the Baltic Sea 2. The route of Wulfstan could not have followed a With onshore winds it is advisable to keep well specific isobath line since a high resolution DBM of offshore until the weather improves before attempting a landfall. (Baltic Pilot 2002:337) the Baltic Sea bottom clearly shows the sinuosity of these lines. In fact, the route that Crumlin-Pedersen proposedcrosses several oftheseisobathsrepresenting If Wulfstan sailed non-stop for seven days and nights, some tens of meters in depth variation—an unlikely and the shortest linear distance between departure and route for a navigator supposedly following a constant arrival points is 390 nautical miles (Nmi), the average depth. minimum speed of his vessel was 2.3 knots (or 55 Nmi 3. Crumlin-Pedersen's route also puts an important for a 24-hour day). The more the vessel departed from this island, Fehmam, on the port side. But this is not straight-line route, the longer the distance it would have mentioned in the Wulfstan text. Furthermore, travelled and the greater the average speed would have been Fehmam was a part of the Wendland until the mid- needed to be to make the voyage in the recorded seven days. 12* century and was not mentioned by Wulfstan Although we do not know Wulfstan's actual travel speed together with the isles under Danish suzerainty to or his routing, the historical account does provide a set of the portside. In the last decades of the U"" century, geographical and temporal constraints within which the Adam of Bremen considered Fehmam integral part voyage took place.