Brandenburg has no useful building stone. The North German Plain is sand and clay, and the great medieval foundations had to invent themselves out of fired brick. Lehnin was a daughter house of Morimond Abbey in Burgundy, but it could not look like Morimond - it had to look like what brick can do. What it does, at scale, is striking. The abbey church rises in the deep red Brick Gothic that defines the architecture of the Hanseatic and Brandenburg world: pointed arches in baked clay, stepped gables, blind arcades, the surface broken into pattern by alternating glazed and unglazed bricks. Lehnin is one of the finest surviving examples in Germany. The church and cloister are largely Romanesque-to-Gothic transitional; the buildings around them date from later restorations, but the religious heart still reads as the late twelfth and thirteenth centuries that built it.

The Cistercians were the medieval Catholic Church's land-development specialists. They were called east into the Slavic margraviates because they cleared swamps, drained fields, founded daughter houses, and turned wilderness into rent. Lehnin did all of this. From its base on the Zauche plateau south of the Havelland it founded Paradies Abbey in 1236 (today Klasztor Paradyz in Poland), Mariensee in 1258 (later relocated to Chorin), and Himmelpfort near Furstenberg in 1299. The Ascanians used the abbey as a tool of the Ostsiedlung, the German eastward settlement that brought Flemish, Frankish, and Saxon farmers into the Slavic borderlands. It was a project of conversion, conquest, and economic transformation - softened in some places, brutal in others - and Lehnin was its religious headquarters in Brandenburg.

Joachim II of Brandenburg, the Hohenzollern elector who had succeeded the Ascanians on the Brandenburg throne, dissolved Lehnin in 1542 during the Reformation. The buildings became a hunting lodge; the Thirty Years' War battered them; the Great Elector Frederick William rebuilt parts as a summer residence for his consort Louise Henriette of Nassau, who died here in 1667. After her death the buildings declined again - used as a stone quarry, ironically, by the same state that had once relied on them as a source of legitimacy. What saved them was the nineteenth-century romantic rediscovery of Gothic ruins. King Frederick William IV of Prussia, who loved medieval architecture the way some kings love hunting, ordered restoration. Between 1871 and 1877 the church was substantially rebuilt, and a place that had nearly been forgotten became a national heritage site again.

In 1911 the Prussian Union of Churches bought the abbey to house the Luise-Henrietten-Stift - a Protestant women's deaconess community whose deaconesses adopted Cistercian customs as a kind of historical homage to the place. The Nazis suppressed them and seized parts of the complex for Wehrmacht and SS use during the war. From 1949 onwards the GDR turned Lehnin into a hospital, and today it operates as a geriatric rehabilitation clinic and nursing home, the church and cloister still maintained as a parish and historical site. Buried under the brick floors are Otto I, Matilda of Groitzsch, Herman and Albert III of Brandenburg-Salzwedel, and Catherine of Saxony - the founding generations of a state that would become Prussia and then Germany. Outside, the village of Lehnin keeps its pace; the Klostersee glints to the north; the wooded plateau rolls away as it has since Otto's reported nap.