The name means what it says: a crossing place used by the Franks. The river gets appended to distinguish it from the far larger Frankfurt am Main. Before there was a Frankfurt there was a West Slavic settlement called Zliwitz, part of the Kingdom of Poland, whose Piast duke Henry the Bearded granted it staple rights in 1225. Construction of St Nicholas Church - today's Friedenskirche - began in 1226. In 1249 the place passed to the Margraviate of Brandenburg, and in 1253 the town received its charter. Control changed hands with the regularity of weather: Pomerania in 1319, Brandenburg again in 1324, the Lands of the Bohemian Crown from 1373 to 1415. What made it rich was traffic. Positioned where the Oder route between Wrocław and Szczecin passed the road west toward Berlin, Frankfurt dominated the river trade of the late Middle Ages, joined the Hanseatic League in 1430, and was stormed by Hussite forces two years later.

In the sixteenth century Polish grain, timber, ash, tar and hemp floated past Frankfurt on the way to Szczecin, and Brandenburg's customs officers took their cut. Then came the Thirty Years' War. In April 1631 a Swedish army stormed the town, destroying much of it including the Georgen Hospital, and won the Battle of Frankfurt an der Oder. The old St Nicholas Church had a stranger fate: secularised, used as a granary, and from the seventeenth century given over to French Huguenot refugees. Russian troops occupied the town briefly in August 1759, just before the slaughter at Kunersdorf a few kilometres east. The nineteenth century restored its commercial swagger - Frankfurt hosted the second-largest annual trade fair in the German Reich, surpassed only by Leipzig - and in 1842 the railway from Berlin arrived.

The town's war record begins before the fighting did. SS Einsatzgruppe VI was assembled in Frankfurt before crossing into Poland in September 1939, where it committed atrocities against Polish civilians in Poznań, Kalisz and Leszno. Throughout the war the Germans brought forced labourers here from Poland and the Soviet Union. In early 1945, columns of prisoners from the dissolved camps at Żabikowo and Świecko were driven on foot through the streets toward Sachsenhausen - death marches whose route ran past ordinary front doors. No battle was ever fought for the town, though it was declared a fortress to slow the Red Army's road to Berlin; the population fled, and the nearly empty city was burned. The border settled on the Oder, the Dammvorstadt became Słubice, and Frankfurt spent forty years as a frontier town of East Germany. In March 2008 the city's Jewish community held its first Torah dedication since the Holocaust, carrying the new scroll from the site of the destroyed Frankfurter Synagogue - five hundred metres from the Polish border - to the Chabad centre, where they danced with it.

Brandenburg's first university opened here in 1506 as the Alma Mater Viadrina, endowed by Elector Joachim I Nestor, and it trained the young Albert of Brandenburg around 1510. The playwright Heinrich von Kleist, born in Frankfurt in 1777, is the city's most famous son. The university closed in 1811, its assets split between two new foundations of King Frederick William III - what became Humboldt University in Berlin, and the university at Breslau, now the University of Wrocław. Then, in 1991, with the border suddenly a seam rather than a wall, Viadrina was refounded with an explicitly European purpose, in close partnership with Adam Mickiewicz University in Poznań. The two jointly run the Collegium Polonicum - on the Polish side, in Słubice - and students take Polish courses free of charge. A German-Polish student residence called Fforst House was described by former university president Gesine Schwan as the place where "Europe begins."

Reunification was not kind to Frankfurt. When the VEB Halbleiterwerk semiconductor plant collapsed it took the local economy with it; by 2003 the only trace of the industry was the IHP microelectronics research institute. The population, above 87,000 at the end of the 1980s, fell to around 58,000 and has since held steady - still the largest German city on the Oder and Brandenburg's fourth-largest after Potsdam, Cottbus and Brandenburg an der Havel. What has grown instead is the relationship across the water. Frankfurt and Słubice have been twinned since 1975 and now run joint projects and shared facilities. Poland entered the European Union in 2004 and the Schengen area at the end of 2007, and the permanent controls on the bridge came down. The Berlin-Warszawa-Express stops at the station, and on hot afternoons everyone goes to Helenesee, a lake inside the city limits that was once, inevitably, a mine.