In the neighbourhood are extensive coal fields. Frankfort-on-the-Oder owes its origin and name to a settlement of Franconian merchants here, in the 13th century, on land conquered by the margrave of Brandenburg from the Wends. In 1253 it was raised to the rank of a town by the margrave John I. and borrowed from Berlin the Magdeburg civic constitution. In 1379 it received from King Sigismund, then margrave of Brandenburg, the right to free navigation of the Oder; and from 1368 to about 1450 it belonged to the Hanseatic League. The university, which is referred to above, was opened by the elector Joachim I. in 1506, was removed in 1516 to Kottbus and restored again to Frankfort in 1539, at which date the Reformation was introduced. It was dispersed during the Thirty Years' War and again restored by the Great Elector, but finally transferred to Breslau in 1811. Frankfort has suffered much from the vicissitudes of war. In the 15th century it successfully withstood sieges by the Hussites (1429 and 1432), by the Poles (1450) and by the duke of Sagan (1477). In the Thirty Years' War it was successively taken by Gustavus Adolphus (1631), by Wallenstein (1633), by the elector of Brandenburg (1634), and again by the Swedes, who held it from 1640 to 1644. During the Seven Years' War it was taken by the Russians (1759). In 1812 it was occupied by the French, who remained till March 1813, when the Russians marched in. See K. R. Hausen, _Geschichte der Universitaet und Stadt Frankfurt_ (1806), and Bieder und Gurnik, _Bilder aus der Geschichte der Stadt Frankfurt-an-der-Oder_ (1898).