The first existence of via Marchionis (VM) was confirmed in the 13th century (1286) 46 as one of the branches of the route running from Frankfurt (Oder) to Pomerelia (Eastern Pomerania) (city of Gdańsk and the castle of the Teutonic Order in Malbork/Marienburg) which split into several smaller parts in western Poland 21, 47, 48, 49. For several centuries this route became a main pathway of migration (Fig. 1) and its particular importance is documented by its former terms – via Regia Prussica or via Regia Nove Marchiae. This implies that the rulers whose lands were crossed by the road were obliged to guarantee the safety of all travelers 50. It was of particular importance during the development of the state of the Teutonic Order in the lands of Prussia, when troops regularly used this route to support the Teutonic Knights, first in the battles with the pagan Prussia “Holy War”, and in the following centuries in wars with Poland and Lithuania 51. The importance of this road in the early modern period is evidenced by the fact that in 1524 the Polish king established customs points between its two branches, which were collecting tolls from passing merchants 52 and in 1549 the VM was described as “great and significant” 53. In the early 19th century, the road became a major factor for the development of the regional economy. Therefore, it was modernized and adapted to modern traffic technologies in the years 1816–1823 through widening up to 5 meters and rubble paving. Before, the road had an irregular course and was strongly dependent on weather conditions 38. This route remained geopolitically important even in the late 19th century, so that the Prussian king Wilhelm IV built a railway line linking Berlin and Königsberg along the same track parallel to the road which was opened in 1873. Thereby, the VM eventually became a modern multiple transport route.
The basic settlement structure was developed on the basis of existing literature and available databases for the 16th century (supplement). In economic analyses we used the king’s estates inventories from 16th to 18th centuries 42, 54, 55 that provide detailed information on the economic situation of rural settlements around Lake Czechowskie over a period of three centuries. Economic inventories gave further information about the use of natural resources in the region. We complemented this information source with other materials, including royal documents 5657. The available written materials focus on the period from 1600 to 1800 for which abundant historical data is available.
Lake Czechowskie varved sediments
Lake Czechowskie (JC) is located about 1,5 km south of the VM in Northern Poland (53o52.2’N, 18o14.1’E, 108 m a.s.l.) and has a surface area of 0.73 km2 and a maximum water depth of 32 m 58. Today, the lake is surrounded by forest, agricultural land and a recreational area. The VM crosses the lake catchment (19.7 km2) in its northern part. The sediments of the lake are seasonally laminated and proven as calcite varves by sediment trap studies 59 which predominantly consist of autochthonous material with only minor contributions of detrital catchment material 20. Microscopic analyses revealed that the varves consist of a seasonal succession of three sublayers commencing in spring with (1) diatom blooms followed by (2) endogenic calcite formation and a final re-suspension layer in autumn that in some years is accompanied by a second diatom bloom (supplement). A robust chronology has been established based on microscopic varve counting, identification of the Askja AD1875 volcanic ash layer, AMS 14C dating of terrestrial plant remains and 137Cs activity concentration measurements 20, 60 (supplement). The excellent varve preservation and mean varve thickness 0.6 -22.4 mm/yr enabled precise sampling in 5-year (varve) intervals for high-resolution pollen analyses.
Environmental reconstruction is mainly based on proxy evidence for landscape openness, agriculture and erosion including selected human pollen indicators, charcoal, and µXRF element scanner data (supplement). In order to obtain quantitative vegetation reconstruction we applied the REVEALS model 61 with the REVEALSinR function 45 (supplement). A key indicator taxon for agriculture practice is secale pollen (rye) (Fig.1), while the sum of non-arboreal pollen from terrestrial plants reflects deforestation. In addition, individual tree taxa allow tracing economic development and forest management practices. For example, Hornbeam (Carpinus) was a major hardwood species for economic development during medieval times and mirrors cultural and economic growth in the region. Pine reflects developments in forest management especially since the late eighteenth century 62. Variations in titanium, measured at sub-annual resolution are a proxy for detrital sediment transport from the catchment into the lake which is interpreted as a measure for erosion processes triggered by anthropogenic changes in vegetation cover.
Societal Impact Index (SII)
We developed a subjective Societal Impact Index (SII) as a measure for anthropogenic pressure on the landscape through combining continuous palaeoecological data (vegetation changes, fire reconstruction, erosion) with non-continuous historical data (foundation of towns, populations in local centers, wars, plagues). From paleoecological data, land coverage of secale was particularly rated because it provides good manifestation of human pressure and modification of the landscape. The SII is an attempt to depict anthropogenic pressure on landscape change.