Reconstructing medieval eroded landscapes of the north-eastern Zuyder Zee (the Netherlands): a refined palaeogeographical time series of the Noordoostpolder between a.d. 1100 and 1400

This paper considers large-scale erosion of late medieval peatland landscapes along the inland lagoon rims of the north-eastern Zuyder Zee area (today: Noordoostpolder, the Netherlands) and integrates palaeogeographical reconstruction, material archeological and spatial archaeohistorical research. The dynamic regional history of coeval loss of peaty coastal plains and boom of maritime activities is studied from archaeological, geological and historical data perspectives. In the first half of the Middle Ages (a.d. 500–1000), vast peatlands and interconnected lakes characterised the study area. During the late Middle Ages (a.d. 1000–1500), increased storm surges and tidal incursions allowed for extensive progressive erosion of inhabited peatlands, transforming the central Netherlands into the Zuyder Zee tidal lagoon. In the north-eastern quadrant of the expanding water body, medieval terrestrial geological and archaeological records fell prey to erosion, re-working and uptake into lagoon-floor deposits. These deposits have been intensively surveyed since the 1940s when the quadrant was reclaimed and made into arable land, and are revealed to contain spatially clustered late medieval archaeological objects.Whereas lagoon floor re-working has hindered making a detailed palaeogeographical reconstruction based on geological data alone, including the mapping of archaeology has helped resolve the pacing of lagoon expansion. The key to resolving the lost peatland palaeogeography for the time frames 1100 and 1400, was to put the archeological data density patterns first and geological lagoon-floor facies descriptions second in process order, while for earlier periods or other regions the opposite order is the convenient choice. We present a map series beginning with an updated map for a.d. 900 (the youngest geological reconstruction), introducing the first detailed palaeogeographical maps for 1100 and 1400 (honouring the late medieval terrestrial and maritime archaeological evidence) and ending with a landscape reconstruction for 1600 (complying with the oldest historical maps of the lagoon), revealing the intertwined landscape history of land and sea as the backdrop for shifts in the human use of both.