Wismar's medieval harbour has been preserved with an authenticity seldom found elsewhere today, conveying an impression of what was in effect the backbone of a medieval maritime trading centre. The Grube (canal) that flows into the harbour is the last remaining manmade medieval waterway in a North German old town quarter. Within the boundaries of the historic town centre three monumental brick churches embody a unique testament to the renowned religious architecture in the Southern Baltic Sea region. The mighty tower of St. Marien Church is today still a landmark of the town from both land and sea.There is many a reminder too of the era of Swedish occupation of the town – the Zeughaus (arsenal), the swedish commander's house as well as the Schwedenköpfe (Swedish busts) guarding the Baumhaus. That era ended permanently in 1903, when after a hundred year pledge agreement expired, Sweden renounced its claim to the town, and it returned to Mecklenburg permanently.